Linear compressor drive device

ABSTRACT

A linear compressor driving apparatus ( 101 ) according to the present invention is a linear compressor driving apparatus having an inverter ( 2 ) which supplies a driving current of a predetermined frequency to a linear compressor ( 100 ), and the apparatus further includes an inverter controller ( 6 ) for controlling the inverter ( 2 ) on the basis of resonance frequency information so that the frequency of an output current from the inverter becomes equal to the resonance frequency, and instantaneous values of an output current Id and an output voltage Vd from the inverter ( 2 ) are measured at a phase timing in which an amount of change in the output current Id of the inverter ( 2 ) becomes zero, and a piston stroke is calculated from these measured values. In such linear compressor driving apparatus ( 101 ), a stroke and a top clearance of the piston of the linear compressor can be accurately detected by relatively simple arithmetic processing, without using a position sensor.

TECHNICAL FIELD

[0001] The present invention relates to a linear compressor drivingapparatus and, more particularly, to an apparatus for driving a linearcompressor which generates a compressed gas in a cylinder by making apiston reciprocate with a linear motor.

BACKGROUND ART

[0002] A linear compressor utilizing a mechanical elastic member orelasticity of a gas has conventionally been known as an apparatus forgenerating a compressed gas.

[0003]FIG. 7 is a cross-sectional view for explaining a conventionallinear compressor, and illustrates a concrete configuration of a linearcompressor using a spring as an elastic member.

[0004] A linear compressor 100 has a cabinet 71 comprising a cylindersection 71 a and a motor section 71 b which are adjacent to each other.The cylinder section 71 a of the cabinet 71 forms a cylindrical-shapedcylinder of the linear compressor. In the cylinder section 71 a, apiston 72 is provided slidably along the direction parallel to a centeraxis of the cylinder (piston axis direction).

[0005] On the back of the piston 72 in the cabinet 71, a piston rod 72 ais placed over the cylinder section 71 a and the motor section 71 b, andan end of the piston rod 72 a is fixed to the piston 72. Further, asupport spring (resonance spring) 81 is placed between the other end ofthe piston rod 72 a and an inner wall 71b1 of the motor section 71 bwhich is opposed to the piston rod 72 a. The support spring 81 deformswhen the piston 72 is displaced from a piston neutral position (pistonreference position), and applies a force to the piston 72 so that thepiston 72 returns to the piston reference position. Further, the pistonneutral position is a piston position where the support spring 81 is notdeformed, and no force is applied from the support spring 82 to thepiston 72 when the piston 72 is located in the piston neutral position.

[0006] Further, a magnet 73 is fixed to a portion of the piston rod 72a, which portion is located in the motor section 71 b, and anelectromagnet 74 comprising an outer yoke 74 a and a stator coilembedded in the outer yoke 74 a is fixed to a portion of the inner wallof the motor section 71 b, which portion is opposed to the magnet 73.

[0007] A linear motor 82 is constituted by the electromagnet 74 and themagnet 73. That is, in the linear compressor 100, the piston 72reciprocates along its axis direction by the driving force of the linearmotor 82, i.e., the electromagnetic force generated between theelectromagnet 74 and the magnet 73, and the elasticity of the supportspring 81.

[0008] On the other hand, a compression chamber 76, which is a closedspace surrounded by a cylinder upper portion inner wall 75, a pistoncompression wall 72 b, and a cylinder peripheral wall 77, is formed atthe cylinder head side of the cabinet 71. An end of a cooling mediuminlet tube la for drawing a low-pressure cooling medium gas into thecompression chamber 76 is opened at the cylinder upper portion innerwall 75 and, further, an end of a cooling medium discharge tube 1 b fordischarging a high-pressure cooling medium gas from the compressionchamber 76 is opened at the cylinder upper portion inner wall 75. Aninlet valve 79 and a discharge valve 80 for preventing back flow of thecooling medium gas are fixed to the cooling medium inlet tube la and thecooling medium discharge tube 1 b, respectively.

[0009] In the linear compressor 100 having the above-describedstructure, the piston 72 reciprocates in its axis direction byintermittent supply of a driving current from a motor driver (not shown)to the linear motor 82, whereby drawing of the low-pressure coolingmedium gas into the compression chamber 76, compression of the coolingmedium gas in the compression chamber 76, and discharge of thecompressed high-pressure cooling medium gas from the compression chamber76 are repeatedly carried out.

[0010] By the way, in the above-mentioned linear compressor 100, evenwhen a current or voltage applied to the linear motor 82 is kept at aconstant value, if the state of load applied onto the linear compressorchanges, the stroke of the piston 72 changes. Therefore, especially in arefrigeration compressor using the linear compressor 100, since thethermodynamic efficiency of refrigerating cycle is significantlyimproved by controlling the flow of cooling medium according to thevarying environmental temperature, a means for detecting the stroke ofthe piston 72 that determines the flow of cooling medium (piston strokedetection means) is needed.

[0011] Further, in the linear compressor 100, from its structuralviewpoint, there is a danger that the front end of the piston mightcollide with the upper wall of the cylinder.

[0012] To be specific, the piston 72 receives not only the pistondriving force of the linear motor 82 and the elasticity of the supportspring 81 but also a force caused by a differential pressure between thepressure of the cooling medium gas in the compression chamber 76 and theback pressure of the piston 72, whereby the center position of thereciprocating motion of the piston 72 (hereinafter also referred to aspiston amplitude center position) is offset with respect to the pistonamplitude center position when the differential pressure is zero, i.e.,the piston position when the support spring is not deformed (pistonneutral position). Therefore, when the internal pressure of thecompression chamber 76 that acts on the piston 72 is increased/decreaseddue to a change of the load state, not only the stroke of the piston 72but also the center position of the reciprocating motion of the piston72 might change.

[0013] In order to prevent collision of the piston with the cylinder,not only the stroke detection means but also a position detection meansfor detecting the distance between the front end of the piston and theinner wall of the cylinder head are indispensable. For example, in alinear compressor having no collision prevention means, the front end ofthe piston hits the inner wall of the cylinder head, resulting inuncomfortable noise or damage to the piston or the cylinder.

[0014] There is employed, as the above-mentioned position detectionmeans, a sensor which can detect the degree of displacement of thepiston (piston displacement) with respect to the piston referenceposition such as the piston neutral position, without contacting themovable members such as the piston in the linear compressor 100. Forexample, a displacement meter using an eddy current system, adisplacement meter using a differential transformer, and the like areemployed.

[0015] However, when such sensor is used, the production cost of thelinear compressor 100 is increased and, moreover, a space for mountingthe sensor is needed, which leads to an increase in the size of thecabinet 71 of the linear compressor 100. Further, since the sensor isused while being exposed to a high-temperature and high-pressure gas inthe compressor 100, there occurs a problem on reliability of the sensoritself, in other words, a problem that a sensor which can be reliablyused under high-temperature and high-pressure atmosphere is desired.

[0016] So, as a method for detecting the position of the piston 72,there is proposed a method of directly measuring the linear motordriving current and voltage which are supplied to the linear compressor100, and deriving the position of the piston 72 on the basis of themeasured values, without using a position sensor placed in the linearcompressor 100 (refer to Japanese Unexamined Patent PublicationNo.Hei.8-508558).

[0017] Hereinafter, a description will be given of a piston positiondetection method used for a linear compressor, which is described in theabove-mentioned literature.

[0018]FIG. 8 is a diagram illustrating an equivalent circuit of a linearmotor for driving a piston of a linear compressor.

[0019] In FIG. 8, L indicates an equivalent inductance [H] of a coil asa component of the linear motor, and R indicates an equivalentresistance [Ω] of the coil. Further, V indicates an instantaneousvoltage [V] applied to the linear motor, and I indicates a current [A]applied to the linear compressor. Further, α×v indicates an inducedelectromotive voltage [V] which is generated when the linear motor isdriven, wherein α is a thrust constant [N/A] of the linear motor, and vis an instantaneous velocity [m/s] of the linear motor.

[0020] The thrust constant α of the linear motor indicates a force [N]which is generated when a unit current [A] is passed through the linearmotor. Although the unit of the thrust constant α is expressed by [N/A],this unit is equivalent to [Wb/m] or [V·s/m].

[0021] The equivalent circuit shown in FIG. 8 is derived from theKirchhoff's law, and an instantaneous velocity v[m/s] of the linearmotor is obtained from the equivalent circuit.

[0022] That is, under the driving state of the linear motor, the voltage(V) applied to the linear motor is balanced with the sum of a droppedvoltage (I×R) [V] due to the equivalent resistance of the coil of thelinear motor, a dropped voltage (L·dI/dt) [V] due to the equivalentinductance of the coil, and the induced electromotive voltage (α×v) [V]generated when driving the linear motor, and the following formula (1)holds. $\begin{matrix}{v = {\frac{1}{\alpha}\left( {V - {R \times I} - {L\frac{I}{t}}} \right)}} & (1)\end{matrix}$

[0023] The coefficients α[N/A], R[Ω], and L[H] used in formula (1) areconstants unique to the motor, and these constants are already-knownvalues. Accordingly, the instantaneous velocity v[m/s] can be obtainedfrom these constants and the applied voltage V[V] and current I[A] whichare measured, on the basis of formula (1).

[0024] Further, a piston displacement (a distance from an undefinedreference position to the piston) x[m] is obtained by time integrationof the instantaneous velocity v[m/s] as represented by the followingformula (2). In formula (2), the constant Const. is the pistondisplacement at the start of integration.

x=∫vdt+Const.  (2)

[0025] As described above, in the piston position detection methoddisclosed in the above-described literature, the measured values V and Iof the applied voltage and current to the linear motor are subjected toarithmetic processing including differentiation based on formula (1) toobtain the instantaneous velocity v of the piston, and further, theinstantaneous velocity v is subjected to arithmetic processing includingintegration based on formula (2), whereby the piston displacement x canbe calculated.

[0026] However, the piston displacement x obtained by the arithmeticprocessing based on formulae (1) and (2) is a displacement withreference to a certain position on the piston axis, and a distance fromthe cylinder head to the piston top dead point position cannot beobtained directly from the displacement x.

[0027] To be specific, when the linear compressor 100 is under loadedcondition, the piston center position (piston amplitude center position)in the piston reciprocating motion is offset with respect to the pistonneutral position (i.e., the piston amplitude center position when thepressure in the compression chamber is equal to the back pressure) bythe pressure of the cooling medium gas, and the piston reciprocatesaround the offset piston amplitude center position. In other words, thepiston displacement x obtained by formula (2) includes an averagecomponent.

[0028] However, every actual analog integrator or digital integratordoes not perform ideal integration processing for outputting a perfectresponse signal with respect to a constant or a DC input, but it isrestricted in responding to a DC input. Therefore, an actual integratorcannot subject the piston displacement x to integration processing inwhich its average component is reflected. The reason why the DC responseof the actual integrator is restricted is because the output of theintegrator should be prevented from being saturated by an unavoidable DCcomponent in the input signal.

[0029] As a result, the piston displacement x[m] obtained by theintegration processing based on formula (2) using an actual integratoris not a displacement from which an actual distance between the pistonand the cylinder head can be directly obtained, but a displacementsimply indicating the piston position with reference to a certain pointon the piston axis.

[0030] Therefore, the piston displacement x[m] obtained from formula (2)is converted into a piston displacement x′ indicating the pistonposition with respect to the piston amplitude center position. Further,using the converted piston displacement x′, arithmetic processing forobtaining a piston displacement x″ with reference to the cylinder headand indicating the piston amplitude center position is carried out.

[0031] Hereinafter, these arithmetic processings will be described indetail.

[0032]FIG. 9 is a diagram schematically illustrating the piston positionin the cylinder.

[0033] Initially, three coordinate systems shown in FIG. 9, i.e., afirst coordinate system X, a second coordinate system X′, and a thirdcoordinate system X″, will be briefly described.

[0034] The first coordinate system X is a coordinate system expressingthe piston displacement x, and it has, as an origin (x=0), a certainpoint Paru on the piston axis. Accordingly, the absolute value of thedisplacement x indicates the distance from the point Paru to the pistonfront end position P.

[0035] The second coordinate system X′ is a coordinate system expressingthe piston displacement x′, and it has, as an origin (x′=0), the pistonamplitude center position Pav. Accordingly, the absolute value of thedisplacement x′ indicates the distance from the amplitude centerposition Pav to the piston front end position P.

[0036] The third coordinate system X″ is a coordinate system expressingthe piston displacement x″, and it has, as an origin (x″=0), thecylinder head position Psh on the piston axis. Accordingly, the absolutevalue of the displacement x″ indicates the distance from the cylinderhead position Psh to the piston front end position P.

[0037] Next, an arithmetic operation for obtaining the pistondisplacement x″ will be described.

[0038] A piston position (piston top dead point position) Ptd in whichthe piston is closest to the cylinder head 75 is indicated by adisplacement xtd on the first coordinate system X, and a piston position(piston bottom dead point position) Pbd in which the piston is farthestfrom the cylinder head 75 is indicated by a displacement xbd on thefirst coordinate system X. Then, a piston stroke Lps[m] is obtained froma difference between the displacement xtd corresponding to the pistontop dead point position Ptd on the first coordinate system X and thedisplacement xbd corresponding to the piston bottom dead point positionPbd on the first coordinate system X.

[0039] Further, the piston amplitude center position Pav in the statewhere the piston is reciprocating is a position which is apart from thedisplacement xtd of the piston position (piston top dead point position)Ptd in which the piston is closest to the cylinder head, by a length(Lps/2) equal to half the piston stroke Lps[m], from the cylinder head.Accordingly, the piston amplitude center position Pav is expressed by adisplacement xav (=(xbd−xtd)/2) on the first coordinate system X.

[0040] Further, when the constant Const. in formula (2) is 0, a newfunction that indicates the piston position P by the piston displacementx′[m] is derived with the piston amplitude center position Pav as areference (origin), in other words, on the second coordinate system X′.

[0041] Subsequently, a description will be given of a method forobtaining the piston displacement x″ indicating the piston amplitudecenter position on the third coordinate system X″ with the cylinder headposition Psh as an origin.

[0042] Under the state where the linear compressor 100 draws in thecooling medium gas (inlet state), i.e., under the state where the inletvalve is open, both of the pressure in the compression chamber and thepressure on the back of the piston are equal to the cooling medium gasinlet pressure. This is because the linear compressor 100 is constructedso that the differential pressure becomes 0 under the state where theinlet valve is open. In this state, a force from the pressure of thecooling medium gas onto the piston can be ignored. That is, in thisstate, the forces acting on the piston are only the repulsive force ofthe spring that is generated by bending of the support spring 81, andthe electromagnetic force that is generated by applying a current to thelinear motor. According to the Newton's law of motion, the sum of theseforces is equal to the product of the total mass of the movable memberthat is moving, and its acceleration.

[0043] Accordingly, under this state, the following formula (3) holds asan equation of motion relating to the movable member.

m×a=α×I−k(x′+xav″−xini″)  (3)

[0044] In formula (3), m is the total mass [kg] of the movable memberthat is reciprocating, a is the instantaneous acceleration [m/s/s] ofthe movable member, and k is the spring constant [N/m] of the supportspring that is incorporated in the linear compressor. Further, xav″ isthe above-mentioned displacement on the third coordinate system X″,which indicates the piston amplitude center position, and the absolutevalue of this displacement xav″ expresses the distance from the cylinderhead position Psh to the piston amplitude center position pav. Further,xini″ is the displacement on the third coordinate system X″, whichindicates the piston neutral position Pini, and the absolute value ofthis displacement xini″ expresses the distance [m] between the pistonneutral position (the position of the piston in the state where thesupport spring is not deformed) Pini and the cylinder head position Psh.

[0045] The instantaneous acceleration a[m/s/s] is obtained as shown inthe following formula (4), by differentiating the instantaneous velocityv[m/s] expressed by formula (1). $\begin{matrix}{a = \frac{v}{t}} & (4)\end{matrix}$

[0046] Furthermore, the displacement x′[m] on the second coordinatesystem X′, which indicates the distance from the piston amplitude centerposition Pav to the piston front end position P, is obtained by settingthe constant Const. in formula (2) at 0.

[0047] Furthermore, the total mass m[kg] of the movable member, thespring constant k[N/m] of the support spring, and the displacement xini″on the third coordinate system X″, which indicates the distance from thecylinder head position Psh to the piston neutral position Pini, arealready known values, and the driving current I may be the measuredvalue.

[0048] Accordingly, the displacement xav″ on the third coordinate systemX″, which indicates the distance from the cylinder head position Psh tothe piston amplitude center position Pav, can be calculated usingformula (3).

[0049] Further, the displacement xtd″[m] on the third coordinate systemX″, which indicates the top dead point position of the piston (theposition where the piston is closest to the cylinder head), can beobtained as a displacement in a position which is apart from thedisplacement xav″ on the third coordinate system X″ obtained by formula(3) (the distance from the cylinder head position Psh to the pistonamplitude center position Pav) by a distance equal to half (Lps/2) thealready-obtained piston stroke length Lps[m], toward the cylinder head.

[0050] In this way, the piston stroke length Lps[m], and thedisplacement xtd″[m] on the third coordinate system X″, which indicatesthe piston top dead point position Ptd as a distance from the cylinderhead position Psh, are calculated from the current I and voltage V whichare applied to the linear compressor.

[0051] However, in the piston position detection method of theconventional linear compressor 100, since the piston displacement x′which relatively indicates the piston position P with reference to thepiston amplitude center position Pav is calculated using the integratorand the differentiator, it is not possible to detect the piston positionwith high accuracy. That is, when the actual integrator anddifferentiator are constituted by analog circuits, ideal operationscannot be expected because of variations in parts, variations incharacteristics due to temperature, and the like. On the other hand,when the integrator and differentiator are constituted by digitalcircuits, ideal operations cannot be expected because of missing of datain sampling and holding.

[0052] Furthermore, when the piston position detecting circuit in thelinear compressor is constituted by digital circuits, it is conceivablethat the measuring cycle of the current I and the voltage V applied tothe linear compressor may be reduced to increase the position detectionaccuracy. However, when the measuring cycle is reduced, the calculationcycle is also reduced, whereby the arithmetic load in the digitalcircuit is increased. Accordingly, when the measuring cycle is reduced,the performance of the microcomputer constituting the digital arithmeticcircuit must be enhanced.

[0053] The present invention is made to solve the above-describedproblems and has for its object to provide a linear compressor drivingapparatus which can detect the position of a piston with high accuracy,on the basis of measured values of a driving current and a drivingvoltage applied to a linear compressor, without increasing loads ofarithmetic processing using these measured values.

DISCLOSURE OF THE INVENTION

[0054] A linear compressor driving apparatus according to the presentinvention (claim 1) is a linear compressor driving apparatus for drivinga linear compressor which has a piston and a linear motor for making thepiston reciprocate, and generates a compressed gas by the reciprocatingmotion of the piston, with an AC voltage being applied to the linearmotor, and this apparatus comprises: an inverter for outputting an ACvoltage and an AC current to the linear motor; a resonance frequencyinformation output means for outputting resonance frequency informationwhich indicates a resonance frequency of the reciprocating motion of thepiston; a voltage detection means for detecting an output voltage of theinverter to output a voltage detection signal; a current detection meansfor detecting an output current of the inverter to output a currentdetection signal; an inverter controller for controlling the inverter onthe basis of the resonance frequency information so that the inverteroutputs, as its output voltage and output current, asinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped currentwhose frequencies match the resonance frequency of the pistonreciprocating motion, respectively; a timing detection means fordetecting, as a specific phase timing, a phase timing at which adifferentiated value of the output current of the inverter becomes zero;and a piston velocity calculation means for receiving the voltagedetection signal and the current detection signal, and calculating amaximum amplitude of a piston velocity in the piston reciprocatingmotion, on the basis of instantaneous values of the output voltage andthe output current from the inverter at the specific phase timing.

[0055] According to the present invention (claim 2), in the linearcompressor driving apparatus defined in claim 1, the timing detectionmeans detects, as the specific phase timing, a phase timing at which theamplitude of the output current from the inverter becomes maximum.

[0056] According to the present invention (claim 3), in the linearcompressor driving apparatus defined in claim 1, the timing detectionmeans detects a phase timing at which the phase of the output AC currentfrom the inverter becomes at least one of 90° and 270°, as the specificphase timing, on the basis of the current detection signal.

[0057] According to the present invention (claim 4), in the linearcompressor driving apparatus defined in claim 3, the inverter isprovided with an inverter controller for outputting an inverter drivingcontrol signal which drives and controls the inverter; and the timingdetection means detects a phase timing at which a differentiated valueof the output current from the inverter becomes zero, on the basis ofthe phase of the inverter driving control signal.

[0058] According to the present invention, (claim 5), in the linearcompressor driving apparatus defined in claim 4, the timing detectionmeans has a phase shift amount detector for detecting the amount ofphase shift of the phase of the inverter driving control signal from thephase of the output current of the inverter, and detects a phase timingat which a differentiated value of the output current of the inverterbecomes zero, on the basis of the inverter driving control signal whosephase is corrected so that the amount of phase shift becomes zero.

[0059] According to the present invention (claim 6), in the linearcompressor driving apparatus defined in claim 1, the piston velocitycalculation means performs a temperature correction process on a thrustconstant of the linear motor, whose value varies with variations intemperature, and calculates a maximum amplitude of the piston velocityon the basis of the temperature-corrected thrust constant, theinstantaneous current value, the instantaneous voltage value, and aninternal resistance value of the linear motor.

[0060] According to the present invention (claim 7), in the linearcompressor driving apparatus defined in claim 1, the piston velocitycalculation means performs a temperature correction process on aninternal resistance value of the linear motor, whose value varies withvariations in temperature, and calculates a maximum amplitude of thepiston velocity on the basis of the temperature-corrected internalresistance value, the instantaneous values of the output voltage andoutput current of the inverter, and a thrust constant of the linearmotor.

[0061] According to the present invention (claim 8), in the linearcompressor driving apparatus defined in claim 1, the piston velocitycalculation means repeats a velocity calculation process for calculatinga maximum amplitude of the piston velocity, and in each of the repeatedvelocity calculation processes, the piston velocity calculation meanscorrects a thrust constant of the linear motor, whose value varies withvariations in the piston velocity, on the basis of a maximum amplitudeof the piston velocity which is calculated in the previous velocitycalculation process, and calculates a maximum amplitude of the pistonvelocity on the basis of the corrected thrust constant.

[0062] According to the present invention (claim 9), the linearcompressor driving apparatus defined in claim 1 further includes astroke information calculation means for calculating piston strokeinformation which indicates a maximum amplitude of a piston displacementin the piston reciprocating motion, on the basis of the output voltageof the inverter and the frequency of the output current of the inverter,which are determined by the inverter controller, and the maximumamplitude of the piston velocity that is calculated by the pistonvelocity calculation means.

[0063] According to the present invention (claim 10), the linearcompressor driving apparatus defined in claim 1 further includes abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity that iscalculated by the piston velocity calculation means.

[0064] According to the present invention (claim 11), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity that iscalculated by the piston velocity calculation means; and an arithmeticmeans for calculating center position information which indicates apiston center position in the piston reciprocating motion, by performingthe four fundamental rules of arithmetic on the basis of the bottom deadpoint position information and the piston stroke information.

[0065] According to the present invention (claim 12), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity which iscalculated by the piston velocity calculation means; and an arithmeticmeans for calculating top dead point position information indicating apiston top dead point position in the piston reciprocating motion, byperforming the four fundamental rules of arithmetic on the basis of thebottom dead point position information and the piston strokeinformation.

[0066] According to the present invention (claim 13), the linearcompressor driving apparatus defined in claim 9 further includes: a topdead point position information detection sensor for detecting a pistontop dead point position in the piston reciprocating motion to output topdead point position information indicating the detected position; and anarithmetic means for calculating center position information indicatinga piston center position in the piston reciprocating motion, byperforming the four fundamental rules of arithmetic on the basis of thetop dead point position information and the piston stroke information.

[0067] According to the present invention (claim 14), the linearcompressor driving apparatus defined in claim 9 further includes: a topdead point position information detection sensor for detecting a pistontop dead point position in the piston reciprocating motion to output topdead point position information indicating the detected position; and anarithmetic means for calculating bottom dead point position informationindicating a piston bottom dead point position in the pistonreciprocating motion, by performing the four fundamental rules ofarithmetic on the basis of the top dead point position information andthe piston stroke information.

[0068] According to the present invention (claim 15), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information detection sensor for detecting apiston bottom dead point position in the piston reciprocating motion;and an arithmetic means for calculating center position informationindicating a piston center position in the piston reciprocating motion,by performing the four fundamental rules of arithmetic on the basis ofthe bottom dead point position information and the piston strokeinformation.

[0069] According to the present invention (claim 16), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information detection sensor for detecting apiston bottom dead point position in the piston reciprocating motion tooutput bottom dead point position information indicating the detectedposition; and an arithmetic means for calculating top dead pointposition information indicating a piston top dead point position in thepiston reciprocating motion, by performing the four fundamental rules ofarithmetic on the basis of the bottom dead point position informationand the piston stroke information.

[0070] According to the present invention (claim 17), the linearcompressor driving apparatus defined in claim 9 further includes: acenter position information calculation means for calculating centerposition information indicating a piston center position in the pistonreciprocating motion, on the basis of the output current from theinverter; and an arithmetic means for calculating top dead pointposition information indicating a piston top dead point position in thepiston reciprocating motion, by performing the four fundamental rules ofarithmetic on the basis of the center position information and thepiston stroke information.

[0071] According to the present invention (claim 18), the linearcompressor driving apparatus defined in claim 9 further includes: acenter position information calculation means for calculating centerposition information indicating a piston center position in the pistonreciprocating motion, on the basis of the output current from theinverter; and an arithmetic means for calculating bottom deal pointposition information indicating a piston bottom dead point position inthe piston reciprocating motion, by performing the four fundamentalrules of arithmetic on the basis of the center position information andthe piston stroke information.

[0072] According to the present invention (claim 19), in the linearcompressor driving apparatus defined in any of claims 10 to 12, thelinear compressor has an elastic member which applies a force to thepiston so as to bring the piston back to its neutral position, when thepiston is displaced from the neutral position; and the bottom dead pointposition information calculation means calculates, as the bottom deadpoint position information, position information indicating the pistonbottom dead point position relative to the piston neutral position, onthe basis of the output voltage of the inverter and the frequency of theoutput current of the inverter, which are determined by the invertercontroller, the maximum amplitude of the piston velocity which iscalculated by the piston velocity calculation means, the weight of themovable member which performs the piston reciprocating motion in thelinear compressor, and the spring constant of the elastic member.

[0073] According to the present invention (claim 20), in the linearcompressor driving apparatus defined in claim 9, the piston strokecalculation means repeats a calculation process for calculating thepiston stroke information on the basis of the maximum amplitude of thepiston velocity, and in each of the repeated calculation processes, thepiston stroke calculation means corrects a thrust constant of the linearmotor, whose value varies with variations in the piston position, on thebasis of the piston stroke information calculated in the previouscalculation process, and calculates the piston stroke information on thebasis of the corrected thrust constant.

[0074] A linear compressor driving apparatus according to the presentinvention (claim 21) is a linear compressor driving apparatus fordriving a linear compressor which has a piston and a linear motor forreciprocating the piston, and generates a compressed gas by thereciprocating motion of the piston, with an AC voltage being applied tothe linear motor, and this apparatus comprises: an inverter foroutputting an AC voltage and an AC current to the linear motor; aresonance frequency information output means for outputting resonancefrequency information that indicates a resonance frequency of the pistonreciprocating motion; a current detection means for detecting an outputcurrent of the inverter to output a current detection signal; aninverter controller for controller the inverter on the basis of theresonance frequency information so that the inverter outputs, as itsoutput voltage and output current, a sinusoidal-wave-shaped voltage anda sinusoidal-wave-shaped current whose frequencies match the resonancefrequency of the piston reciprocating motion, respectively; a timingdetection means for detecting, as a specific phase timing, a phasetiming at which a differentiated value of the output current of theinverter becomes zero; and a piston center position calculation meansfor calculating position information indicating a piston center positionin the piston reciprocating motion, on the basis of an instantaneousvalue of the output current of the inverter at the specific phasetiming, with reference to a piston position where a pressure differencebetween the pressure of a cooling medium gas that is discharged from thelinear compressor and the pressure of the cooling medium gas that isdrawn into the linear compressor becomes zero.

[0075] According to the present invention (claim 22), in the linearcompressor driving apparatus defined in claim 21, the linear compressorhas an elastic member which applies a force to the piston so as to bringthe piston back to its neutral position, when the piston is displacedfrom the neutral position; and the center position informationcalculation means calculates, as the center position information,position information indicating the piston center position relative tothe piston neutral position, on the basis of the maximum amplitude ofthe output current from the inverter, the thrust constant of the linearmotor, and the spring constant of the elastic member.

[0076] According to the present invention (claim 23), the linearcompressor driving apparatus defined in claim 21 further includes: adischarge pressure detection means for detecting the pressure of thecooling medium gas that is discharged from the linear compressor; and aninlet pressure detection means for detecting the pressure of the coolingmedium gas that is drawn into the linear compressor; wherein the centerposition information calculation means calculates an action force in thedirection of the piston reciprocating motion, which force acts on thepiston from the cooling medium gas, on the basis of the pressuredifference between the discharge pressure and the inlet pressure, andthen calculates, as the center position information, positioninformation indicating the piston center position relative to the pistonposition where the pressure difference becomes zero, on the basis of thecalculated action force.

[0077] According to the present invention (claim 24), in the linearcompressor driving apparatus defined in claim 23, the center positioninformation calculation means calculates an action force in thedirection of the piston reciprocating motion, which force acts on thepiston from the cooling medium gas, on the basis of the pressuredifference between the discharge pressure and the inlet pressure, andthe resonance frequency indicated by the resonance frequencyinformation, and then calculates, as the center position information,position information indicating the piston center position relative tothe piston position where the pressure difference becomes zero, on thebasis of the calculated action force.

[0078] As described above, according to the present invention (claim 1),there is provided a linear compressor driving apparatus for driving alinear compressor which has a piston and a linear motor for making thepiston reciprocate, and generates a compressed gas by the reciprocatingmotion of the piston, with an AC voltage being applied to the linearmotor, and this apparatus comprises: an inverter for outputting an ACvoltage and an AC current to the linear motor; a resonance frequencyinformation output means for outputting resonance frequency informationwhich indicates a resonance frequency of the reciprocating motion of thepiston; a voltage detection means for detecting an output voltage of theinverter to output a voltage detection signal; a current detection meansfor detecting an output current of the inverter to output a currentdetection signal; an inverter controller for controlling the inverter onthe basis of the resonance frequency information so that the inverteroutputs, as its output voltage and output current, asinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped currentwhose frequencies match the resonance frequency of the pistonreciprocating motion, respectively; a timing detection means fordetecting, as a specific phase timing, a phase timing at which adifferentiated value of the output current of the inverter becomes zero;and a piston velocity calculation means for receiving the voltagedetection signal and the current detection signal, and calculating amaximum amplitude of a piston velocity in the piston reciprocatingmotion, on the basis of instantaneous values of the output voltage andthe output current from the inverter at the specific phase timing.Therefore, a displacement of the piston can be easily and accuratelyobtained on the basis of the driving current and driving voltage of thelinear compressor, without using complicated calculations such asintegration and differentiation.

[0079] According to the present invention (claim 2), in the linearcompressor driving apparatus defined in claim 1, the timing detectionmeans detects, as the specific phase timing, a phase timing at which theamplitude of the output current from the inverter becomes maximum.Therefore, in an arithmetic formula for calculating the piston velocityfrom the driving current and driving voltage of the linear compressor, aterm including the differentiated value of the driving current can bedeleted as being zero.

[0080] According to the present invention (claim 3), in the linearcompressor driving apparatus defined in claim 1, the timing detectionmeans detects a phase timing at which the phase of the output AC currentfrom the inverter becomes at least one of 90° and 270°, as the specificphase timing, on the basis of the current detection signal. Therefore,in an arithmetic formula for calculating the piston velocity from thedriving current and driving voltage of the linear compressor, a termincluding the differentiated value of the driving current can be deletedas being zero.

[0081] According to the present invention (claim 4), in the linearcompressor driving apparatus defined in claim 3, the inverter isprovided with an inverter controller for outputting an inverter drivingcontrol signal which drives and controls the inverter; and the timingdetection means detects a phase timing at which a differentiated valueof the output current from the inverter becomes zero, on the basis ofthe phase of the inverter driving control signal. Therefore, in anarithmetic formula for calculating the piston velocity from the drivingcurrent and driving voltage of the linear compressor, a term includingthe differentiated value of the driving current can be deleted.

[0082] According to the present invention (claim 5), in the linearcompressor driving apparatus defined in claim 4, the timing detectionmeans has a phase shift amount detector for detecting the amount ofphase shift of the phase of the inverter driving control signal from thephase of the output current of the inverter, and detects a phase timingat which a differentiated value of the output current of the inverterbecomes zero, on the basis of the inverter driving control signal whosephase is corrected so that the amount of phase shift becomes zero.Therefore, a phase timing at which the differentiated value of theoutput current of the inverter becomes zero can be correctly detected,on the basis of the inverter driving control signal.

[0083] According to the present invention (claim 6), in the linearcompressor driving apparatus defined in claim 1, the piston velocitycalculation means performs a temperature correction process on a thrustconstant of the linear motor, whose value varies with variations intemperature, and calculates a maximum amplitude of the piston velocityon the basis of the temperature-corrected thrust constant, theinstantaneous current value, the instantaneous voltage value, and aninternal resistance value of the linear motor. Therefore, the maximumamplitude of the piston velocity can always be detected with accuracy,irregardless of variations in the thrust constant of the linear motordue to variations in the temperature of the linear compressor.

[0084] According to the present invention (claim 7), in the linearcompressor driving apparatus defined in claim 1, the piston velocitycalculation means performs a temperature correction process on aninternal resistance value of the linear motor, whose value varies withvariations in temperature, and calculates a maximum amplitude of thepiston velocity on the basis of the temperature-corrected internalresistance value, the instantaneous values of the output voltage andoutput current of the inverter, and a thrust constant of the linearmotor. Therefore, the maximum amplitude of the piston velocity canalways be detected with accuracy, irregardless of variations in theinternal resistance value of the linear motor due to variations in thetemperature of the linear compressor.

[0085] According to the present invention (claim 8), in the linearcompressor driving apparatus defined in claim 1, the piston velocitycalculation means repeats a velocity calculation process for calculatinga maximum amplitude of the piston velocity, and in each of the repeatedvelocity calculation processes, the piston velocity calculation meanscorrects a thrust constant of the linear motor, whose value varies withvariations in the piston velocity, on the basis of a maximum amplitudeof the piston velocity which is calculated in the previous velocitycalculation process, and calculates a maximum amplitude of the pistonvelocity on the basis of the corrected thrust constant. Therefore, themaximum amplitude of the piston velocity can always be detected withaccuracy, irregardless of variations in the thrust constant of thelinear motor due to variations in the piston velocity.

[0086] According to the present invention (claim 9), the linearcompressor driving apparatus defined in claim 1 further includes astroke information calculation means for calculating piston strokeinformation which indicates a maximum amplitude of a piston displacementin the piston reciprocating motion, on the basis of the output voltageof the inverter and the frequency of the output current of the inverter,which are determined by the inverter controller, and the maximumamplitude of the piston velocity that is calculated by the pistonvelocity calculation means. Therefore, the driving ability of the linearcompressor can be controlled on the basis of the piston strokeinformation.

[0087] According to the present invention (claim 10), the linearcompressor driving apparatus defined in claim 1 further includes abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity that iscalculated by the piston velocity calculation means. Therefore, theamount of flexure of the resonance spring can be grasped according tothe piston bottom dead point position information. Thereby, drivingcontrol of the linear compressor can also be carried out on the basis ofthe amount of flexure of the resonance spring so that the resonancespring is not deformed beyond the destruction limits.

[0088] According to the present invention (claim 11), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity that iscalculated by the piston velocity calculation means; and an arithmeticmeans for calculating center position information which indicates apiston center position in the piston reciprocating motion, by performingthe four fundamental rules of arithmetic on the basis of the bottom deadpoint position information and the piston stroke information. Therefore,the linear compressor can be controlled on the basis of the pistoncenter position information so that the piston vibration center positionmatches the position where the maximum efficiency of the linear motorcan be achieved, whereby the linear compressor driving efficiency can befurther enhanced.

[0089] According to the present invention (claim 12), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity which iscalculated by the piston velocity calculation means; and an arithmeticmeans for calculating top dead point position information indicating apiston top dead point position in the piston reciprocating motion, byperforming the four fundamental rules of arithmetic on the basis of thebottom dead point position information and the piston strokeinformation. Therefore, the possibility of collision between the pistonand the cylinder head can be judged with high accuracy, on the basis ofthe top dead point position information.

[0090] According to the present invention (claim 13), the linearcompressor driving apparatus defined in claim 9 further includes: a topdead point position information detection sensor for detecting a pistontop dead point position in the piston reciprocating motion to output topdead point position information indicating the detected position; and anarithmetic means for calculating center position information indicatinga piston center position in the piston reciprocating motion, byperforming the four fundamental rules of arithmetic on the basis of thetop dead point position information and the piston stroke information.Therefore, the linear compressor can be controlled using a simple sensorso that the piston vibration center position matches the position wherethe maximum efficiency of the linear motor can be achieved, whereby thelinear compressor driving efficiency can be further enhanced.

[0091] According to the present invention (claim 14), the linearcompressor driving apparatus defined in claim 9 further includes: a topdead point position information detection sensor for detecting a pistontop dead point position in the piston reciprocating motion to output topdead point position information indicating the detected position; and anarithmetic means for calculating bottom dead point position informationindicating a piston bottom dead point position in the pistonreciprocating motion, by performing the four fundamental rules ofarithmetic on the basis of the top dead point position information andthe piston stroke information. Therefore, the linear compressor can becontrolled using a simple sensor so that the resonance spring is notdeformed beyond the destruction limits, on the basis of the pistonbottom dead point position information.

[0092] According to the present invention (claim 15), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information detection sensor for detecting apiston bottom dead point position in the piston reciprocating motion;and an arithmetic means for calculating center position informationindicating a piston center position in the piston reciprocating motion,by performing the four fundamental rules of arithmetic on the basis ofthe bottom dead point position information and the piston strokeinformation. Therefore, the linear compressor can be controlled using asimple sensor so that the piston vibration center position matches theposition where the maximum efficiency of the linear motor can beachieved, whereby the linear compressor driving efficiency can befurther enhanced.

[0093] According to the present invention (claim 16), the linearcompressor driving apparatus defined in claim 9 further includes: abottom dead point position information detection sensor for detecting apiston bottom dead point position in the piston reciprocating motion tooutput bottom dead point position information indicating the detectedposition; and an arithmetic means for calculating top dead pointposition information indicating a piston top dead point position in thepiston reciprocating motion, by performing the four fundamental rules ofarithmetic on the basis of the bottom dead point position informationand the piston stroke information. Therefore, the risk of collisionbetween the piston and the cylinder head can be judged on the basis ofthe top dead point position information, using a simple sensor.

[0094] According to the present invention (claim 17), the linearcompressor driving apparatus defined in claim 9 further includes: acenter position information calculation means for calculating centerposition information indicating a piston center position in the pistonreciprocating motion, on the basis of the output current from theinverter; and an arithmetic means for calculating top dead pointposition information indicating a piston top dead point position in thepiston reciprocating motion, by performing the four fundamental rules ofarithmetic on the basis of the center position information and thepiston stroke information. Therefore, the possibility of collisionbetween the piston and the cylinder head can be judged with highaccuracy, on the basis of the top dead point position information.

[0095] According to the present invention (claim 18), the linearcompressor driving apparatus defined in claim 9 further includes: acenter position information calculation means for calculating centerposition information indicating a piston center position in the pistonreciprocating motion, on the basis of the output current from theinverter; and an arithmetic means for calculating bottom deal pointposition information indicating a piston bottom dead point position inthe piston reciprocating motion, by performing the four fundamentalrules of arithmetic on the basis of the center position information andthe piston stroke information. Therefore, driving control of the linearcompressor can also be carried out so that the resonance spring is notcompressed beyond the destruction limits, on the basis of the pistonbottom dead point position information.

[0096] According to the present invention (claim 19), in the linearcompressor driving apparatus defined in any of claims 10 to 12, thelinear compressor has an elastic member which applies a force to thepiston so as to bring the piston back to its neutral position, when thepiston is displaced from the neutral position; and the bottom dead pointposition information calculation means calculates, as the bottom deadpoint position information, position information indicating the pistonbottom dead point position relative to the piston neutral position, onthe basis of the output voltage of the inverter and the frequency of theoutput current of the inverter, which are determined by the invertercontroller, the maximum amplitude of the piston velocity which iscalculated by the piston velocity calculation means, the weight of themovable member which performs the piston reciprocating motion in thelinear compressor, and the spring constant of the elastic member.Therefore, the amount of flexure of the resonance spring can be graspedaccording to the piston bottom dead point position information. Thereby,driving control of the linear compressor so as to prevent the resonancespring from being deformed beyond the destruction limits can be easilycarried out on the basis of the amount of flexure of the resonancespring.

[0097] According to the present invention (claim 20), in the linearcompressor driving apparatus defined in claim 9, the piston strokecalculation means repeats a calculation process for calculating thepiston stroke information on the basis of the maximum amplitude of thepiston velocity, and in each of the repeated calculation processes, thepiston stroke calculation means corrects a thrust constant of the linearmotor, whose value varies with variations in the piston position, on thebasis of the piston stroke information calculated in the previouscalculation process, and calculates the piston stroke information on thebasis of the corrected thrust constant. Therefore, the maximum amplitudeof the piston velocity can always be detected with accuracy,irregardless of variations in the thrust constant of the linear motordue to variations in the piston position.

[0098] According to the present invention (claim 21), there is provideda linear compressor driving apparatus for driving a linear compressorwhich has a piston and a linear motor for reciprocating the piston, andgenerates a compressed gas by the reciprocating motion of the piston,with an AC voltage being applied to the linear motor, and this apparatuscomprises: an inverter for outputting an AC voltage and an AC current tothe linear motor; a resonance frequency information output means foroutputting resonance frequency information that indicates a resonancefrequency of the piston reciprocating motion; a current detection meansfor detecting an output current of the inverter to output a currentdetection signal; an inverter controller for controller the inverter onthe basis of the resonance frequency information so that the inverteroutputs, as its output voltage and output current, asinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped currentwhose frequencies match the resonance frequency of the pistonreciprocating motion, respectively; a timing detection means fordetecting, as a specific phase timing, a phase timing at which adifferentiated value of the output current of the inverter becomes zero;and a piston center position calculation means for calculating positioninformation indicating a piston center position in the pistonreciprocating motion, on the basis of an instantaneous value of theoutput current of the inverter at the specific phase timing, withreference to a piston position where a pressure difference between thepressure of a cooling medium gas that is discharged from the linearcompressor and the pressure of the cooling medium gas that is drawn intothe linear compressor becomes zero. Therefore, the linear compressor canbe controlled on the basis of the piston center position information sothat the piston vibration center position matches the position where themaximum efficiency of the linear motor can be achieved, whereby thelinear compressor driving efficiency can be further enhanced.

[0099] According to the present invention (claim 22), in the linearcompressor driving apparatus defined in claim 21, the linear compressorhas an elastic member which applies a force to the piston so as to bringthe piston back to its neutral position, when the piston is displacedfrom the neutral position; and the center position informationcalculation means calculates, as the center position information,position information indicating the piston center position relative tothe piston neutral position, on the basis of the maximum amplitude ofthe output current from the inverter, the thrust constant of the linearmotor, and the spring constant of the elastic member. Therefore, thelinear compressor can be controlled on the basis of the piston centerposition information so that the piston vibration center positionmatches the position where the maximum efficiency of the linear motorcan be achieved, whereby the linear compressor driving efficiency can befurther enhanced.

[0100] According to the present invention (claim 23), the linearcompressor driving apparatus defined in claim 21 further includes: adischarge pressure detection means for detecting the pressure of thecooling medium gas that is discharged from the linear compressor; and aninlet pressure detection means for detecting the pressure of the coolingmedium gas that is drawn into the linear compressor; wherein the centerposition information calculation means calculates an action force in thedirection of the piston reciprocating motion, which force acts on thepiston from the cooling medium gas, on the basis of the pressuredifference between the discharge pressure and the inlet pressure, andthen calculates, as the center position information, positioninformation indicating the piston center position relative to the pistonposition where the pressure difference becomes zero, on the basis of thecalculated action force. Therefore, the linear compressor can becontrolled on the basis of the piston center position information sothat the piston vibration center position matches the position where themaximum efficiency of the linear motor can be achieved, whereby thelinear compressor driving efficiency can be further enhanced.

[0101] According to the present invention (claim 24), in the linearcompressor driving apparatus defined in claim 23, the center positioninformation calculation means calculates an action force in thedirection of the piston reciprocating motion, which force acts on thepiston from the cooling medium gas, on the basis of the pressuredifference between the discharge pressure and the inlet pressure, andthe resonance frequency indicated by the resonance frequencyinformation, and then calculates, as the center position information,position information indicating the piston center position relative tothe piston position where the pressure difference becomes zero, on thebasis of the calculated action force. Therefore, the linear compressorcan be controlled on the basis of the piston center position informationthat the piston vibration center position matches the position where themaximum efficiency of the linear motor can be achieved, whereby thelinear compressor driving efficiency can be further enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0102]FIG. 1 is a block diagram for explaining a linear compressordriving apparatus according to a first embodiment of the presentinvention.

[0103] FIGS. 2(a)-2(d) are diagrams illustrating concrete circuitconstructions of inverters to be employed in the linear compressordriving apparatus according to the first embodiment, illustrating avoltage type full bridge inverter (FIG. 2(a)), a current type fullbridge inverter (FIG. 2(b)), and voltage type half bridge inverters(FIGS. 2(c) and 2(d)).

[0104]FIG. 3 is a diagram illustrating the phases of pistondisplacement, piston velocity, and piston acceleration with respect tothe phase of driving current, in the resonance driving state of a linearcompressor driven by the linear compressor driving apparatus accordingto the first embodiment.

[0105]FIG. 4 is a block diagram for explaining a linear compressordriving apparatus according to a second embodiment of the presentinvention.

[0106]FIG. 5 is a block diagram for explaining a linear compressordriving apparatus according to a third embodiment of the presentinvention.

[0107]FIG. 6 is a block diagram for explaining a linear compressordriving apparatus according to a fourth embodiment of the presentinvention.

[0108]FIG. 7 is a cross-sectional view for explaining a common linearcompressor.

[0109]FIG. 8 is a diagram illustrating an equivalent circuit of a linearmotor as one of components of the linear compressor.

[0110]FIG. 9 is a diagram schematically illustrating a piston positionin a cylinder of the linear compressor.

[0111]FIG. 10 is a diagram for explaining operations of the linearcompressor driving apparatus according to the third and fourthembodiments.

BEST MODE TO EXECUTE THE INVENTION

[0112] Initially, the fundamental principle of the present inventionwill be briefly described.

[0113] Under a resonance driving state of a linear compressor wherein alinear compressor is driven in a resonance state of piston reciprocatingmotion, a state where the phase of an AC current (driving current)applied to the linear compressor matches a phase corresponding to thevelocity of the reciprocating piston, is maintained. That is, in theresonance driving state, the amplitude of the piston velocity of thelinear compressor becomes maximum at a timing when the differentiatedvalue of the linear compressor driving current becomes 0.

[0114] The inventors of the present invention have noticed therelationship between the phase of the linear motor driving current andthe phase of the piston velocity in the resonance driving state of theliner compressor, and found that the maximum amplitude of the pistonvelocity can be detected with high accuracy by detecting a phase timingat which the differentiated value of the linear compressor drivingcurrent becomes 0, and that the piston top dead point position can becalculated from the maximum amplitude of the piston velocity.

[0115] Hereinafter, embodiments of the present invention will bedescribed.

[0116] (Embodiment 1)

[0117]FIG. 1 is a block diagram for explaining a linear compressordriving apparatus according to a first embodiment of the presentinvention.

[0118] A linear compressor driving apparatus 101 according to the firstembodiment is an apparatus for driving a linear compressor 100 which isconstituted such that the piston reciprocating motion is in theresonance state when the frequency of the piston reciprocating motion isa frequency (resonance frequency) Fr.

[0119] To be specific, the linear compressor driving apparatus 101includes a power supply 1 which generates a DC voltage VDC as a powersupply voltage; an inverter 2 which converts the power supply voltageVDC into an AC voltage Vd of a predetermined frequency, and outputs itto the linear compressor 100; a current sensor 9 which monitors aninverter output current Id that is output from the inverter 2 to thelinear compressor 100; an output current detection means 3 which detectsthe inverter output current Id from the inverter 2 on the basis of themonitor output Scm; and an output voltage detection means 4 whichdetects an inverter output voltage Vd that is output from the inverterto the linear compressor 100.

[0120] The linear compressor driving apparatus 101 further includes aresonance frequency information output means 5 which outputs resonancefrequency information Irf indicating the resonance frequency Fr of thepiston reciprocating motion; an inverter controller 6 which controls theinverter 2 according to an inverter control signal Scp so that thefrequency Fid of the output current Id matches the resonance frequencyFr, on the basis of the resonance frequency information Irf; a timingdetection means 7 which detects a phase timing when the differentiatedvalue of the output current Id from the inverter 2 (the driving currentof the linear compressor 100) becomes 0, on the basis of the monitoroutput Scm from the current sensor 9.

[0121] The linear compressor driving apparatus 101 further includes apiston velocity calculation means 8 which calculates the maximumamplitude (maximum velocity) of the piston velocity, on the basis of adetection result (driving voltage detection signal) Dvd from the outputvoltage detection means 4, and a detection result (driving currentdetection signal) Dcd from the output current detection means 3; and anopen/close switch 10 which controls supply and stop of supply of thedriving voltage detection signal Dvd and the driving current detectionsignal Dcd to the piston velocity calculation means 8, on the basis of adetection result Scs from the timing detection means 7.

[0122] Subsequently, the respective components of the linear compressordriving apparatus will be described in detail.

[0123] Initially, the resonance frequency information output means 5will be described.

[0124] In this first embodiment, as described above, the linearcompressor 100 is designed so as to have a constant resonance frequencyFr as the resonance frequency of the piston reciprocating motion, underthe load conditions with which the compressor 100 operates, and theresonance frequency information output means 5 outputs resonancefrequency information Irf indicating this specific resonance frequency.

[0125] However, the resonance frequency information output means 5 isnot restricted to the above-mentioned one which outputs informationindicating the specific resonance frequency Fr that is previously set onthe linear compressor 100.

[0126] For example, in the linear compressor 100 shown in FIG. 7, thespring force which is generated by the compressed cooling medium gas andacts on the piston is large, and the spring force significantly variesdepending on the operating state of the linear compressor 100, e.g., thepressure of the compressed cooling medium gas or the displacement of thepiston 72. Therefore, actually, the resonance frequency of the linearcompressor 100 cannot be uniquely determined.

[0127] So, the resonance frequency information output means 5 maymonitor the state of the compressed cooling medium gas, estimate aresonance frequency appropriate to the state, and output informationindicating the estimated resonance frequency. As a method for estimatinga resonance frequency appropriate to the state of the cooling mediumgas, a resonance frequency may be calculated from variables indicatingthe state of the cooling medium gas (e.g., the pressure and temperatureof the cooling medium) on the basis of a predetermined functionalequation, or a resonance frequency may be estimated from variables withreference to a table indicating correspondences between the variablesand resonance frequencies.

[0128] Furthermore, as described in a specification of Japanese PatentApplication No. 2000-361301, under a condition that the amplitude of anAC current to be inputted to the linear compressor 100 as its drivingcurrent is constant, a frequency at which power consumption by thelinear compressor becomes maximum when the frequency of the AC currentis varied, may be estimated as a reference frequency.

[0129] Next, the inverter controller 6, the inverter 2, and the inputpower supply 1 of the inverter 2 will be described in detail.

[0130] The inverter controller 6 outputs, to the inverter 2, a PWM(Pulse Width Modulation) signal for switching the inverter 2 as acontrol signal Scp for the inverter 2, and controls the pulse width ofthe PWM signal Scp on the basis of the resonance frequency informationIrf. The PWM signal Scp drives the inverter 2 for a period correspondingto the pulse width.

[0131] The inverter 2 receives a voltage VDC from the power supply 1,and supplies an AC voltage Vd and an AC current Id whose frequencies areequal to the resonance frequency Fr, to the linear compressor 1, on thebasis of the inverter control signal Scp supplied from the invertercontroller 6. Although a DC power supply for supplying a DC voltage tothe inverter 2 is necessary as the input power supply 1 for the inverter2, the input power supply for the inverter 2 may be a commercial ACpower supply. Such input power supply is composed of a rectifier circuitfor rectifying a commercial AC voltage (current) such as a diode bridgecircuit or a high strength converter, and a smoothing condenser forsmoothing the output of the rectifier circuit.

[0132] There are various kinds of concrete circuit structures of theinverter 2 as shown in FIGS. 2(a)˜2(d).

[0133] The inverters shown in FIGS. 2(a) and 2(b) are a voltage typefull bridge inverter 21 and a current type full bridge inverter 22,respectively, each having four switching elements, and diodescorresponding to the respective switching elements. Each of these fullbridge inverters outputs a voltage in a range from +V_(DC) to −V_(DC),to a load L, when the voltage of its input power supply is a DC voltageV_(DC).

[0134] To be specific, the voltage type full bridge inverter 21 iscomposed of a first series connection circuit C1 a in which first andsecond switching circuits 21 a and 21 b are connected in series, and asecond series connection circuit C1 b in which third and fourthswitching circuits 21 c and 21 d are connected in series, and the secondseries connection circuit C1 b is connected in parallel with the firstseries connection circuit C1 a. Each of the respective switchingcircuits 21 a˜21 d is composed of a switching element S1 comprising anNPN transistor, and a diode D1 which is connected in reverse-parallelwith the switching element S1. In the inverter 21, the DC voltage VDCfrom the power supply 1 is applied to both ends of the first and secondseries connected circuits C1 a and C1 b, and the AC voltage Vd to beapplied to the load L is generated between a node N1 a of the first andsecond switching circuits 21 a and 21 b in the first series connectioncircuit C1 a, and a node N1 b of the third and fourth switching elements21 c and 21 d in the second series connection circuit C1 b.

[0135] Further, the current type full bridge inverter 22 is composed ofa first series connection circuit C2 a in which first and secondswitching circuits 22 a and 22 b are connected in series; a secondseries connection circuit C2 b in which third and fourth switchingcircuits 22 c and 22 d are connected in series, which circuit C2 b isconnected in parallel with the first series connection circuit C2 a; andan inductance element 22 e, an end of which is connected to ends of thefirst and second series connection circuits C2 a and C2 b. Each of therespective switching circuits 22 a˜22 d is composed of a switchingelement S2 comprising an NPN transistor, and a diode D2 whose anode isconnected to an emitter of the NPN transistor. In this inverter 22, whenthe DC voltage VDC from the power supply 1 is applied between the otherend of the inductance element 22 e and the other ends of the first andsecond series connection circuits C2 a and C2 b, the AC voltage Vd to beapplied to the load L is generated between a node N2 a of the first andsecond switching circuits 22 a and 22 b in the first series connectioncircuit C2 a, and a node N2 b of the third and fourth switching circuits22 c and 22 d in the second series connection circuit C2 b.

[0136] Further, the inverters shown in FIGS. 2(c) and 2(d) are voltagetype half bridge inverters 23 and 24, respectively, each comprising twoswitching elements, and diodes corresponding to the respective switchingelements.

[0137] The half bridge inverter 23 outputs a voltage in a range from+V_(DC)/2 to −V_(DC)/2, to the load L, when the voltage at its inputpower supply is the DC voltage V_(DC). Further, the half bridge inverter24 outputs a voltage in a range from +V_(DC) to 0 when the voltage atits input power supply is the DC voltage V_(DC). In this way, theutilization factor of the power supply by the half bridge inverter ishalf that of the full bridge inverter.

[0138] To be specific, the voltage type half bridge inverter 23 iscomposed of a first series connection circuit C3 a in which first andsecond switching circuits 23 a and 23 b are connected in series, and asecond series connection circuit C3 b in which first and secondcapacitance circuits 23 c and 23 d are connected in series, and thesecond series connection circuit C3 b is connected in parallel with thefirst series connection circuit C3 a. Each of the respective switchingcircuits 23 a˜23 d is composed of a switching element S3 comprising anNPN transistor, and a diode D3 which is connected in reverse-parallelwith the switching element S3. The first and second capacitance circuits23 c and 23 d comprise condensers 23 c and 23 d, respectively. In thisinverter 23, when the DC voltage VDC from the power supply 1 is appliedto both ends of the first and second series connected circuits C3 a andC3 b, the AC voltage Vd to be applied to the load L is generated betweena node N3 a of the first and second switching circuits 23 a and 23 b inthe first series connection circuit C3 a, and a node N3 b of the firstand second capacitance circuits 23 c and 24 d in the second seriesconnection circuit C3 b.

[0139] Further, the voltage type half bridge inverter 24 is composed ofa series connection circuit C4 a in which first and second switchingcircuits 24 a and 24 b are connected in series. Each of the switchingcircuits 24 a and 24 b is composed of a switching element S4 comprisingan NPN transistor, and a diode D4 which is connected in inverse-parallelwith the switching element S4. In the inverter 24, when the outputvoltage from the DC power supply 1 is applied to both ends of the seriesconnection circuit C4 a, the AC voltage Vd to be applied to the load Lis generated between an anode and a cathode of the diode D4 which is acomponent of the second switching circuit 24 a.

[0140] Next, the output current detection means 3, the current sensor 9,the output voltage detection means 4, the open/close switch 10, and thetiming detection means 7 will be described in detail.

[0141] The output current detection means 3 detects the inverter outputcurrent (linear compressor driving current) Id applied to the linearmotor 82 (refer to FIG. 7) of the linear compressor 100, on the basis ofthe driving current monitor signal Scm as a monitor output of thecurrent sensor 9, and outputs a driving current detection signal Dcd tothe open/close switch 10. As an example of the current sensor 9, thereis a magnetic type current detection sensor using a magnetic substanceand a Hall element, or a current transformer which generates a voltageaccording to the linear compressor driving current. Further, as a methodfor detecting the driving current of the linear compressor 100, there isa method of calculating a current from a voltage which is generated in ashunt resistor placed in the current supply path.

[0142] The output voltage detection means 4 detects the inverter outputvoltage (linear compressor driving voltage) Vd to be supplied from theinverter 2 to the linear motor 82 (refer to FIG. 7) of the linearcompressor 100, and outputs a driving voltage detection signal Dvd tothe open/close switch 10. When the inverter 2 is a voltage typeinverter, since the waveform of the inverter output voltage Vd is a PWMwaveform, it is difficult to directly measure the inverter outputvoltage Vd. So, as a method for measuring the output voltage from thevoltage type inverter, there is a method of subjecting the outputvoltage to PWM waveform shaping, using a low-pass filter comprising atransformer or a condenser and a resistor, and measuring thewaveform-shaped output voltage. Further, as a method for measuring theoutput voltage from the voltage type inverter, besides theabove-mentioned method using a low-pass filter, there is a method ofcalculating the output voltage Vd of the inverter 2, on the basis of theDC voltage VDC inputted to the inverter 2, and the pulse width of thePWM signal that is the inverter control signal Scp outputted from theinverter controller 6.

[0143] The open/close switch 10 has a first input side node 10 a towhich the driving current detection signal Dcd from the output currentdetection means 3 is input; a second input side node 10 b to which thedriving voltage detection signal Dvd from the output voltage detectionmeans 4 is input; a first output side node 10 c for outputting thedriving current detection signal Dcd to the piston velocity detectionmeans 8; and a second output side node 10 d for outputting the drivingvoltage detection signal Dvd to the piston velocity detection means 8.The open/close switch 10 connects or isolates the first input side node10 a to/from the first output side node 10 c, and connects or isolatesthe second input side node 10 c to/from the first output side node 10 d.

[0144] The timing detection means 7 detects a phase timing at which thephase of the linear compressor driving current Id matches at least oneof 90° and 270°, on the basis of the driving current monitor signal Scmfrom the current sensor 9, and outputs a switch control signal Scs forconnecting the first (second) input side node 10 a (10 b) to the first(second) output side node 10 c (10 d), at the phase timing, to theopen/close switch 10. This timing detector 7 utilizes that the inverteroutput current (linear compressor driving current) Id is a sinusoidalwave and therefore it takes an extreme value when the phase is 90° or270°, and detects a phase timing at which the phase of the drivingcurrent matches at least one of 90° and 270° as a phase timing at whichthe driving current Vd takes a peak value (maximum amplitude).

[0145] Finally, the piston velocity calculation means 8 will bedescribed in detail.

[0146] The piston velocity calculation means 8 receives the drivingcurrent detection signal Dcd from the output current detection means 3and the driving voltage detection signal Dvd from the output voltagedetection means 4 at the phase timing detected by the timing detector 7,and calculates the maximum amplitude of the velocity of the piston thatreciprocates at a constant angular velocity (the maximum value of theabsolute value of the piston velocity) from the instantaneous values ofthe inverter output current Id and the inverter output voltage Vd at thephase timing, and the thrust constant of the linear motor, and outputspiston velocity information Ipve indicating the maximum amplitude of thepiston velocity.

[0147] Subsequently, the arithmetic processing to be performed by thepiston velocity calculation means 8 will be specifically described withreference to drawings and formulae.

[0148]FIG. 3 is a diagram for explaining the resonance driving state ofthe linear compressor wherein the linear compressor is driven in theresonance state of piston reciprocating motion, and illustrates how thedriving current Id, piston velocity (reciprocation velocity) v, pistondisplacement x′, and piston acceleration a change in the resonancedriving state. The piston displacement x′ is a displacement of thepiston position with respect to the piston amplitude center position Pavshown in FIG. 9.

[0149] Since the inverter output current (linear motor driving current)Id supplied to the linear compressor 100 is in proportion to the forceapplied to the piston, the phase of the linear motor driving current Idis equal to the phase of the piston velocity v in the resonance drivingstate of the linear compressor 100. Further, since the pistondisplacement x′ and the piston acceleration a correspond to anintegrated value and a differentiated value of the piston velocity v,respectively, the phase of the piston displacement x′ is delayed by 90°with respect to the phase of the piston velocity v, and the phase of thepiston acceleration a is advanced by 90° with respect to the pistonvelocity v, in the resonance driving state of the linear compressor.

[0150] Further, as for the equation of motion of the piston, formula (1)holds, which is derived from the equivalent circuit of the linear motor(refer to FIG. 8) according to the Kirchhoff's law, as already explainedfor the prior art. However, as the equation of motion of the piston inthe resonance driving state of the linear compressor, the followingformula (5) especially holds instead of formula (1). $\begin{matrix}{{Vm} = {\frac{1}{\alpha}\left( {V_{1} - {R \times I_{1}}} \right)}} & (5)\end{matrix}$

[0151] To be brief, as shown in FIG. 3, in the resonance driving statewhere the linear compressor 100 is driven in the resonance state of thepiston reciprocating motion, the phase of the linear motor drivingcurrent Id is equal to the phase of the piston velocity v. For example,when the phase of the driving current Id is 90° or 270°, the phase ofthe piston velocity v is also 90° or 270°.

[0152] To be specific, in the resonance driving state of the linearcompressor 100, the piston velocity v takes its maximum value or minimumvalue, i.e., the absolute value of the piston velocity becomes maximum,at the phase timing detected by the timing detection means 7 (the timingat which the phase of the driving current Id is 90° or 270°), and thedriving current Id also takes its maximum value or minimum value.Therefore, the differentiated value of the driving current Id becomeszero, whereby the value of the third term in the right side of formula(1) becomes zero.

[0153] Accordingly, when the linear compressor is in the resonancedriving state, formula (5), which is obtained by deleting the third termin the right side of formula (1), holds. A variable V and a variable Iin formula (5) are a measured value V of the inverter output voltage Vdand a measured value I of the inverter output current Id, respectively.

[0154] Based on formula (5), the maximum amplitude (the maximum value orminimum value) v0[m/s] of the piston velocity v is obtained from theinstantaneous value V1[V] of the inverter output voltage Vd (measuredvalue V) at the timing when the phase of the driving current of thelinear compressor is 90° or 270°, the instantaneous value I1[A] of theinverter output current Id (measured value I) at this timing, theequivalent resistance R [Ω] of the coil as a component of the linearmotor, and the thrust constant α [N/A] of the motor.

[0155] In the linear compressor driving apparatus 101 according to thefirst embodiment, the respective means 3˜5, 7, and 8 as components ofthe linear compressor driving apparatus 101, and the inverter controller6 are constituted by software. However, these means 3˜5, 7, and 8, andthe inverter controller 6 may be constituted by hardware.

[0156] Further, in the description of the first embodiment, forsimplification, the linear compressor driving apparatus 101 has theopen/close switch 10 constituted by hardware. However, when therespective means 3˜8 are constituted by software, the linear compressordriving apparatus 101 can be constituted without using the open/closeswitch 10.

[0157] For example, instead of using the open/close switch 10, theoutput current detection means 3 and the output voltage detection means4 may be operated only when the timing detection means 7 detects a phasetiming at which the phase of the linear compressor driving current Idmatches at least one of 90° and 270° to output the driving currentdetection signal Dcd and the driving voltage detection signal Dvd to thepiston velocity detection means 8, respectively.

[0158] Next, the operation will be described.

[0159] The inverter controller 6 generates a pulse signal Scp whosepulse width is adjusted according to the resonance frequency informationIrf outputted from the resonance frequency information output means 5,and supplies the pulse signal Scp as an inverter control signal to theinverter 2. The pulse width of the pulse signal Scp is adjusted so thatthe linear compressor 100 is driven in the resonance state of the pistonreciprocating motion.

[0160] When the pulse signal Scp is supplied to the inverter 2, theinverter 2 generates an AC voltage Vd whose frequency matches theresonance frequency Fr, from the DC voltage V_(DC) supplied from thepower supply 1, on the basis of the pulse signal Scp, and outputs the ACvoltage Vd to the linear motor of the linear compressor 100 as itsdriving voltage.

[0161] For example, when the voltage type full bridge inverter 21 shownin FIG. 2(a) is used as the inverter 2, the pulse signal Scp from theinverter controller 6 is applied to the bases of the NPN transistors(switching elements) S1 constituting the respective switching circuits21 a˜21 d in the inverter 21. In the inverter 21, ON/OFF operations ofthe switching elements S1 of the first and fourth switching circuits 21a and 21 d, and ON/OFF operations of the switching elements S1 of thesecond and third switching circuits 21 b and 21 c are complementarycarried out. Thereby, an AC voltage as the inverter output voltage Id isgenerated between the connection node N1 a of the first seriesconnection circuit C1 a and the connection node N1 b of the secondseries connection circuit C1 b, and this AC voltage Id is applied as adriving voltage to the linear motor of the linear compressor 100.

[0162] In the linear compressor 100, when the driving voltage Id isapplied to the linear motor, the piston starts reciprocating motion.Thereafter, when the driving state of the linear compressor 100 isstabilized, the linear compressor 100 goes into the resonance drivingstate where the piston reciprocating motion is in the resonance state,under a predetermined load condition.

[0163] At this time, the driving current Id supplied to the linearcompressor is monitored by the current sensor 9, and the current sensor9 outputs a current monitor output (driving current monitor signal) Scmto the output current detection means 3 and the timing detection means7.

[0164] In the output current detection means 3, the inverter outputcurrent, i.e., the driving current Id of the linear compressor 100, isdetected on the basis of the current monitor output Scs from the currentsensor 9, and a detection result (driving current detection signal) Dcdis output to the first input side node 10 a of the open/close switch 10.Further, in the output voltage detection means 4, the inverter outputvoltage Vd is detected, and a detection result (driving voltagedetection signal) Dvd is output to the second input side node 10 b ofthe open/close switch 10.

[0165] In the timing detection means 7, the phase timing at which thephase of the driving current Id becomes 90° or 270° is detected on thebasis of the current monitor output Scm from the current sensor 9 and,at this phase timing, the switch control signal Scs for connecting thefirst and second input side nodes 10 a and 10 b of the open/close switch10 with the corresponding first and second output side nodes 10 c and 10d is output to the open/close switch 10.

[0166] In the open/close switch 10, the corresponding input side nodeand output side node are connected at the phase timing according to theswitch control signal Scs, and the values (instantaneous values) I1 andV1 of the driving current Id and the driving voltage Vd at the phasetiming are output to the piston velocity calculation means 8.

[0167] In the piston velocity calculation means 8, a crest value vm ofthe piston velocity is calculated from the instantaneous values I1 andV1 of the driving current and the driving voltage at the phase timing,on the basis of formula (5) described above, and piston velocityinformation Ipve indicating the crest value is output.

[0168] As described above, in the linear compressor driving apparatus101 according to the first embodiment, the linear compressor 100 isdriven under the resonance driving state where the piston reciprocatingmotion is in the resonance state, and the instantaneous value V1[V] ofthe driving voltage and the instantaneous value I1[A] of the drivingcurrent when the phase of the linear compressor driving current Id underthis driving state becomes 90° or 270° are measured, and further, themaximum amplitude vm [m/s] of the piston velocity is obtained on thebasis of a predetermined function expression, using the measuredinstantaneous value V1[V] of driving voltage and the measuredinstantaneous value I1[A] of driving current, the equivalent resistance[Ω] of the coil of the linear motor, and the thrust constant α [N/A] ofthe motor. Therefore, the number of times the driving current ismeasured is reduced as compared with the case where the piston velocityis obtained by performing differentiation based on the measured value ofthe linear compressor driving current, and the maximum amplitude vm[m/s] of the piston velocity can be obtained by measuring the drivingcurrent and the driving voltage once for every cycle of the drivingcurrent, at the minimum.

[0169] Furthermore, in this first embodiment, since the maximumamplitude vm of the piston velocity is calculated by the fourfundamental rules of arithmetic using the driving current instantaneousvalue I1[A] and the driving voltage instantaneous value V1[V] at thetiming when the phase of the driving current Id is 90° or 270°, it isnot necessary to perform differentiation of the driving current incalculating the maximum amplitude of the piston velocity. Therefore,calculation errors caused by a differentiator are eliminated to enhancethe piston velocity calculating accuracy.

[0170] While in this first embodiment the timing detection means 7detects a phase timing at which the phase of the inverter output current(linear compressor driving current) Id becomes at least one of 90° and270°, the timing detection means 7 may detect a phase timing at whichthe amount of change in the driving current Id of the linear compressor100 becomes zero.

[0171] Also in this case, the timing detector 7 outputs a phase timingat which the instantaneous value of the driving current (inverter outputcurrent) Id becomes the crest value (maximum amplitude). The reason isas follows. Since the driving current is a sinusoidal wave, the drivingcurrent takes its peak value when the phase of the driving current is90° and 270°.

[0172] Furthermore, as a method of detecting a timing at which thedriving current (inverter output current) Id takes its crest value,there is proposed a method of continuously monitoring the value of theinverter output current, and detecting a phase timing at which thedirection of change of this value is switched, i.e., a phase timing atwhich the direction of change of the output current value is switchedfrom increase to decrease or from decrease to increase.

[0173] Furthermore, while in this first embodiment the timing detectionmeans 7 detects a phase timing at which the phase of the output currentfrom the inverter 2 becomes 90° or 270°, on the basis of the monitoroutput Scm of the current sensor 9, the timing detection means 7 maydetect a phase timing at which the phase of the output current from theinverter 2 becomes 90° or 270°, on the basis of the pulse signal Scpwhich is a control signal for the inverter 2 outputted from the invertercontroller 6.

[0174] In this case, however, there is a possibility that the phase ofthe inverter output current which is theoretically determined from thecontrol signal (pulse signal) Scp for the inverter 2 outputted from theinverter controller 6 might be deviated from the phase of the outputcurrent Id which is actually output from the inverter 2 by an amountequivalent to a control error.

[0175] So, there is proposed a method of detecting a phase differencebetween the phase of the ideal inverter output current based on theinverter control signal Scp outputted from the inverter controller 6 andthe phase of the output current Id actually outputted from the inverter2, and correcting the phase of the inverter control signal Scp from theinverter controller 6 on the basis of the detected phase difference. Asa concrete method of detecting such phase difference, there is proposeda method of measuring a phase timing at a zero cross point of the outputcurrent Id which is actually output from the inverter 2, and calculatinga difference between this phase timing and a phase timing at which thephase of the inverter control signal Scp from the inverter controller 6becomes 0° or 180°.

[0176] Further, while in this first embodiment the internal resistancevalue R of the linear motor to be used in the arithmetic processing bythe piston velocity calculation means 8 is a specific value that ismeasured in advance, the internal resistance value R may be subjected tocorrection based on temperature.

[0177] To be brief, actually, the internal resistance value R of thelinear motor increases as the temperature of the linear motor increases.

[0178] So, a more accurate value can be obtained as a crest value of thepiston velocity by measuring the temperature of the linear motor, andusing a value obtained by subjecting a previously measured internalresistance value to correction based on the temperature, in the pistonvelocity calculation.

[0179] As a concrete method for temperature-correcting the internalresistance value, there is proposed a method using a table showing therelationships between the temperatures of conductors to be used as thecoil of the linear motor and their resistance values, or a method usinga calculation formula for temperature-correcting the internal resistancevalue.

[0180] For example, when the coil of the linear motor is a copper coilthat is generally used, a resistance value Rt at t° C. in relation to aresistance value R20 measured at 20° C., can be obtained by thefollowing formula (6).

[0181] ddd

Rt=R 20{1+0.00393×(t−20)}  (6)

[0182] Further, while in this first embodiment the thrust constant ofthe linear motor to be used in the arithmetic processing by the pistonvelocity calculation means 8 is a specific value that is measured inadvance, the thrust constant may be subjected to correction according tothe driving state of the linear compressor.

[0183] For example, the thrust constant may be subjected to correctionaccording to the temperature of the linear motor. That is, actually, thethrust constant decreases as the temperature of the linear motorincreases. This is because the flux density of the magnetic substanceused in the linear motor decreases as the temperature increases. So, amore accurate value can be obtained as the crest value of the pistonvelocity by measuring the temperature of the linear motor, and using avalue obtained by subjecting a previously measured thrust constant tocorrection based on the temperature, in the piston velocity calculation.As a concrete method for subjecting the thrust constant to temperaturecorrection, there is proposed a method using a table showing therelationships between the temperatures of available magnetic substancesand their flux densities.

[0184] Furthermore, the thrust constant may be subjected to correctionaccording to the driving velocity (angular velocity) of the linearmotor. That is, actually, the thrust constant of the linear motordecreases as the driving velocity (angular velocity) of the linear motorincreases. So, the piston velocity calculation means 8, which repeatedlycalculates the piston velocity, may correct the thrust constant of thelinear motor on the basis of the piston velocity obtained by theprevious calculation in each of the calculation steps repeated, and itmay calculate the piston velocity using the corrected thrust constant.As a concrete method for correcting the thrust constant, there isproposed a method of correcting the thrust constant of the linear motorusing a table showing the relationships between the driving velocitiesof the motor and the thrust constants thereof, which are obtained fromtest values.

[0185] (Embodiment 2)

[0186]FIG. 4 is a block diagram for explaining a linear compressordriving apparatus according to a second embodiment of the presentinvention.

[0187] A linear compressor driving apparatus 102 according to the secondembodiment is provided with, in addition to the linear compressordriving apparatus 101 according to the first embodiment, a piston strokecalculation means 41 which calculates the stroke of piston reciprocatingmotion on the basis of the crest value v0 of the piston velocity that isobtained by the piston velocity calculation means 8, and the inverterdriving frequency Fd that is determined by the inverter controller 6,and outputs piston stroke information Ipst indicating the piston stroke.The inverter controller 6 according to this second embodiment adjuststhe pulse width of the PWM signal Scp for switching the inverter 2, onthe basis of the resonance frequency information Irf, and outputs thepulse width adjusted PWM signal Scp as an inverter driving controlsignal and, furthermore, outputs information (inverter driving frequencyinformation) Idf indicating the output voltage of the inverter 2 and thefrequency of the output voltage, which are determined according to thepulse width of the PWM signal Scp, as the inverter driving frequency Fd,to the piston stroke calculation means 41. Ideally, the inverter drivingfrequency Fd matches the resonance frequency information Fr. Further, inthis second embodiment, the piston stroke calculation means 41 isconstituted by software. However, the piston stroke calculation means 41may be constituted by hardware.

[0188] Next, the operation will be described.

[0189] Since the operations of the components of the linear compressordriving apparatus 102 according to this second embodiment except theinverter controller 6 and the piston stroke calculation means 41 areidentical to those already described for the linear compressor drivingapparatus 101 according to the first embodiment, the operations of theinverter controller 6 and the piston stroke calculation means will bemainly described hereinafter.

[0190] The position of the piston 72 that reciprocates in the linearcompressor 100 is expressed by a sinusoidal function in which time is avariable, as the piston 72 is subjected to the pressure of thecompressed cooling medium gas. Accordingly, assuming that the angularvelocity of piston reciprocating motion is ω[rad/sec], the maximumamplitude of piston displacement is xm[m], and the piston displacementrelative to the piston amplitude center position Pav (refer to FIG. 9)(i.e., the distance between the point where the piston is positioned attime t, and the piston amplitude center position) is x(t)[m], the pistondisplacement x(t) is represented by the following formula (7), with timet[sec] being a variable.

x(t)=x _(m)×sin ω·t  (7)

[0191] Further, the piston velocity is also expressed by a sinusoidalfunction in which time is a variable. Accordingly, like the pistondisplacement, assuming that the angular velocity of the pistonreciprocating motion is ω[rad/sec], the maximum amplitude of the pistonvelocity is vm[m/s], and the piston instantaneous velocity (the pistonvelocity at time t) is v(t)[m/s], the piston instantaneous velocity v(t)is represented by a sinusoidal function in which time t[sec] is avariable, as shown by the following formula (8).

v(t)=v _(m)×sin ω·t  (8)

[0192] Further, since the piston displacement x(t) is an integratedvalue of the piston velocity v(t), the following formula (9) is derivedfrom formula (8), as a functional equation indicating the pistondisplacement with time being a variable. $\begin{matrix}\begin{matrix}{{x(t)} = {\int{{v(t)}{t}}}} \\{= {\frac{v_{m}}{\omega} \times \left( {{- \sin}\quad {\omega \cdot t}} \right)}}\end{matrix} & (9)\end{matrix}$

[0193] Then, the piston displacement x(t) is erased from formulae (7)and (9), whereby the maximum amplitude xm of the piston displacement canbe expressed using the maximum amplitude vm of the piston velocity, asxm=−vm/ω.

[0194] Accordingly, the maximum amplitude xm[m] of the pistondisplacement can be obtained by dividing the maximum amplitude vm[m/s]of the piston velocity, with the operating angular velocity ω[rad/sec].

[0195] That is, in the inverter controller 6, the pulse width of the PWMsignal Scp for switching the inverter 2 is adjusted on the basis of theresonance frequency information Irf, and the pulse width adjusted PWMsignal Scp is output to the inverter 2 as an inverter driving controlsignal, and further, the information (inverter driving frequencyinformation) Idf indicating the output voltage of the inverter 2 and thefrequency of the output voltage, which are determined according to thepulse width of the PWM signal Scp, is output as the inverter drivingfrequency Fd to the piston stroke calculation means 41.

[0196] Then, on receipt of the piston velocity information Ipveoutputted from the piston velocity calculation means 8 and the inverterdriving frequency information Idf outputted from the inverter controller6, the piston stroke calculation means 41 performs arithmetic processingin which the maximum amplitude vm[m/s] of the piston velocity indicatedby the piston velocity information Ipve is divided by the angularvelocity ω[rad/sec] of the piston reciprocating motion. Thereby, themaximum amplitude xm[m] of the piston displacement is calculated. Theangular velocity ω[rad/sec]of the piston reciprocating motion can beobtained by multiplying the output voltage of the inverter 2 and thefrequency Fd[Hz] of the output voltage which are indicated by theinverter driving frequency information Idf, with 2π.

[0197] Then, the calculation means 41 outputs the piston strokeinformation Ipst indicating the piston stroke in the pistonreciprocating motion (double the amplitude maximum value xm), asinformation indicating the maximum amplitude xm[m] of the pistondisplacement, which is obtained in the above-described arithmeticprocessing.

[0198] As described above, the linear compressor driving apparatus 102according to the second embodiment includes, in addition to thecomponents of the linear compressor driving apparatus 101 according tothe first embodiment, the piston stroke calculation means 41 forcalculating the piston stroke on the basis of the crest value vm of thepiston velocity obtained by the piston velocity calculation means 8, andthe inverter driving frequency Fd determined from the resonancefrequency Fr of the linear compressor. Therefore, the risk of collisionbetween the piston and the cylinder head in the linear compressor can bejudged on the basis of the piston stroke.

[0199] While the linear compressor driving apparatus 102 according tothe second embodiment is constituted by adding the piston strokecalculation means 41 to the linear compressor driving apparatus 101according to the first embodiment, the linear compressor drivingapparatus 102 may further include a bottom dead point positioninformation output means for outputting information about the distancefrom the cylinder head position Psh to the piston bottom dead pointposition Pbd (i.e., the displacement xbd″ in the third coordinate systemX″ shown in FIG. 9) as information indicating the piston bottom deadpoint position Pbd (refer to FIG. 9), and an arithmetic means forperforming four fundamental operations of arithmetic on the basis of thepiston stroke information and the bottom dead point positioninformation.

[0200] In this case, the arithmetic means can derive the pistondisplacement xav″ in the third coordinate system X″ indicating thepiston amplitude center position pav (refer to FIG. 9), by subtracting avalue (Lps/2) half the stroke value indicated by the piston strokeinformation, from the value xbd″ indicated by the bottom dead pointposition information (refer to FIG. 9). Furthermore, in this case, thelinear compressor driving efficiency can be further enhanced bycontrolling the linear compressor so that the piston amplitude centerposition matches a position where the maximum efficiency of the linearmotor can be achieved.

[0201] Further, the piston displacement xtd″ on the third coordinatesystem X″ indicating the piston top dead point position Ptd (refer toFIG. 9) can be derived by subtracting the piston stroke value (Lps)itself indicated by the piston stroke information, from the value xbd″indicated by the bottom dead point position information (refer to FIG.9), with the arithmetic means. Since this displacement xtd″ is thedistance from the cylinder head to the piston top dead point position,the possibility of collision of the piston with the cylinder head can bejudged from the displacement and, therefore, it is useful in preventingcollision of the piston with the cylinder head.

[0202] As a concrete configuration of the bottom dead point positioninformation output means, for example, there is a bottom dead pointposition sensor which measures, as a piston bottom point position, aposition where a predetermined measurement point that is set on thepiston is most apart from the cylinder head, and outputs the measuredvalue as information indicating the distance from the cylinder headposition Psh to the piston bottom dead point position Pbd. Further, thebottom dead point position sensor may be a position sensor having ashort range of measurement, which can detect only the piston bottom deadpoint position, or a simple position sensor which detects whether or notthe piston measurement point goes away from the cylinder head beyond apredetermined position.

[0203] Furthermore, the bottom dead point position information outputmeans may output bottom dead point position information indicating apiston bottom dead point position in the piston reciprocating motionwith reference to the cylinder head position psh, on the basis of theoutput voltage of the inverter and the frequency of the output currentof the inverter, which are determined by the inverter controller, andthe maximum amplitude of the piston velocity, which is calculated by thepiston velocity calculation means.

[0204] Moreover, the bottom dead point position information output meansmay output, as the bottom dead point position information, positioninformation indicating the piston bottom dead point with reference tothe piston neutral position, on the basis of the output voltage of theinverter and the frequency of the output current of the inverter, whichare determined by the inverter controller, the maximum amplitude of thepiston velocity which is calculated by the piston velocity calculationmeans, the weight of the movable member performing the pistonreciprocating motion, and the spring constant of the elastic member. Aconcrete configuration of the bottom dead point position informationoutput means in this case will be later described as a bottom dead pointposition calculation means 51 (refer to FIG. 5) according to a thirdembodiment.

[0205] Furthermore, the linear compressor driving apparatus may include,in addition to the linear compressor driving apparatus 102 according tothe second embodiment, a top dead point position output means foroutputting information about the distance from the cylinder headposition Psh to the piston top dead point position Ptd (the displacementxtd″ in the third coordinate system X″ shown in FIG. 9), as informationindicating the piston top dead point position Ptd (refer to FIG. 9), andan arithmetic means for performing four fundamental operations ofarithmetic on the basis of the piston stroke information and the topdead point position information.

[0206] In this case, the arithmetic means can derive the pistondisplacement xav″ in the third coordinate system X″ indicating thepiston amplitude center position pav (refer to FIG. 9), by adding avalue (Lps/2) half the stroke value indicated by the piston strokeinformation, to the value xbd″ indicated by the bottom dead pointposition information (refer to FIG. 9).

[0207] Further, the displacement xpd″ in the third coordinate system X″indicating the piston bottom dead point position Pbd (refer to FIG. 9)can be derived by adding the piston stroke value (Lps) indicated by thepiston stroke information to the value xtd″ indicated by the top deadpoint position information (refer to FIG. 9), with the arithmetic means.Since this displacement xbd″ is the distance from the cylinder headposition Psh to the piston bottom dead point position Pbd, thedisplacement xbd″ is useful in drive control for the linear compressorto prevent the resonance spring from being deformed beyond thedestruction limit.

[0208] As a concrete configuration of the top dead point positioninformation output means, for example, there is a top dead pointposition sensor which measures, as a piston top point position, aposition where a predetermined measurement point that is set on thepiston is closest to the cylinder head, and outputs the measured valueas information indicating the distance from the cylinder head positionPsh to the piston top dead point position Ptd. Further, the top deadpoint position sensor may be a position sensor having a short range ofmeasurement, which can detect only the piston top dead point position,or a simple position sensor which merely detects whether or not themeasurement point of the piston approaches the cylinder head beyond apredetermined position.

[0209] Furthermore, the linear compressor driving apparatus may include,in addition to the linear compressor driving apparatus 102 according tothe second embodiment, an amplitude center position informationcalculation means for outputting the distance from the cylinder headposition Psh to the piston amplitude center position pav (thedisplacement xav″ in the third coordinate system X″ shown in FIG. 9) asinformation indicating the piston amplitude center position Pav (referto FIG. 9), and an arithmetic means for performing four fundamentaloperations of arithmetic on the basis of the piston stroke informationand the amplitude center position information.

[0210] In this case, the arithmetic means can derive the displacementxpd″ in the third coordinate system X″ indicating the piston bottom deadpoint position Pbd (refer to FIG. 9), by adding a value (Lps/2) half thestroke value indicated by the piston stroke information, to the valuexav″ indicated by the amplitude center position information (refer toFIG. 9).

[0211] Further, conversely, the arithmetic means can derive thedisplacement xtd″ in the third coordinate system X″ indicating thepiston top dead point position Ptd (refer to FIG. 9), by subtracting avalue (Lps/2) half the stroke value indicated by the piston strokeinformation, from the value xav″ indicated by the amplitude centerposition information (refer to FIG. 9).

[0212] As a method of calculating the information indicating theamplitude center position (the distance from the cylinder head positionPsh to the piston amplitude center position Pav), there is a method ofcalculating a force caused by the gas pressure applied to the piston, onthe basis of the pressure difference between the discharge pressure andthe inlet pressure of the linear compressor, and the Bohr cross-sectionof the piston, to calculate the piston amplitude center position.

[0213] In the above-described amplitude center position informationcalculating method using the pressure difference, a force caused by thegas pressure applied to the piston may be calculated using not only thepressure difference but also the linear compressor driving frequency co,whereby the distance information as the piston amplitude center positioninformation can be calculated with higher accuracy.

[0214] Moreover, while in this second embodiment the thrust constant ofthe linear motor to be used in the arithmetic processing by the pistonvelocity calculation means is a specific value that is previouslymeasured, the thrust constant may be subjected to correction accordingto the piston amplitude center position.

[0215] That is, actually, the magnetic flux density between the coil andthe magnet in the linear motor is increased or decreased according tothe positional relationship between the coil and the magnet. This isbecause the magnetic field caused by the current applied to the linearmotor increases or decreases the magnetic field of the magnet.

[0216] So, the amplitude center position information calculation meansmay correct the value of the thrust constant on the basis of theamplitude center position information which has been obtained in theprevious calculation step, in each of calculation steps of amplitudecenter position information to be repeated, and it may calculate theamplitude center position information on the basis of the correctedthrust constant.

[0217] Further the piston stroke calculation means 8 may repeatedlycalculate the piston stroke information on the basis of the maximumamplitude of the piston velocity, and correct the value of the thrustconstant of the linear motor, which value varies according to the pistonposition, on the basis of the piston stroke information calculated inthe previous calculation step, in each of calculation steps to berepeated, and further, calculate the piston stroke information on thebasis of the corrected thrust constant. In this case, a more accuratevalue can be derived as the piston stroke.

[0218] (Embodiment 3)

[0219]FIG. 5 is a block diagram for explaining a linear compressordriving apparatus according to a third embodiment of the presentinvention. FIG. 10 illustrates a coordinate system Y″ showing a pistonposition relative to a piston neutral position, in contrast with acoordinate system X″ (the third coordinate system shown in FIG. 9)indicating a piston position relative to a cylinder header position Psh.

[0220] The linear compressor driving apparatus 103 according to thethird embodiment includes, in addition to the components of the linearcompressor driving apparatus 101 according to the first embodiment, abottom dead point position calculation means 51 which calculates adisplacement ybd″ of a piston bottom dead point position Pd relative toa piston neutral position Pav (refer to FIG. 10), as distanceinformation between the piston neutral position Pav and the pistonbottom dead point position Pbd, on the basis of the crest value vm ofthe piston velocity obtained by the piston velocity calculation means 8,and the inverter driving frequency Fd determined by the invertercontroller 6, and outputs the distance information as piston bottom deadpoint position information Ibdc. The piston neutral position Pav is aposition of the piston 72 on the piston axis when the support spring isnot deformed. Further, the inverter controller 6 according to this thirdembodiment adjusts the pulse width of the PWM signal Scp for switchingthe inverter 2 on the basis of the resonance frequency information Irf,and outputs the pulse width adjusted PWM signal Scp as an inverterdriving control signal to the inverter 2 and, furthermore, outputsinformation (inverter driving frequency information) Idf indicating theoutput voltage of the inverter 2 and the frequency of the output currentof the inverter 2, which are determined according to the pulse width ofthe PWM signal Scp, as the inverter driving frequency Fd, to the bottomdead point position calculation means 51.

[0221] Ideally, the inverter driving frequency Fd matches the resonancefrequency information Fr. Further, in this third embodiment, the bottomdead point position calculation means 51 is constituted by software.However, the bottom dead point position calculation means 51 may beconstituted by hardware.

[0222] Next, the operation will be described.

[0223] Since the operations of the components of the linear compressordriving apparatus 103 according to this third embodiment except theinverter controller 6 and the bottom dead point position calculationmeans 51 are identical to those already described for the linearcompressor driving apparatus 101 according to the first embodiment, theoperations of the inverter controller 6 and the bottom dead pointposition calculation means 51 will be mainly described hereinafter.

[0224] As a motion equation relating to the piston reciprocating motionby the linear motor of the linear compressor 103, the following equation(10) holds.

m×a+k×y″=α×I−β(P _((t)) −P _(S))  (10)

[0225] In equation (10), m is the total mass [kg] of the reciprocatingmovable member, and a is the instantaneous acceleration [m/s/s] of thereciprocating movable member. Further, k is the spring constant [N/m] ofthe support spring that is incorporated into the linear compressor, y″is the displacement [m] of the movable member with respect to theposition (piston neutral position) Pini of the movable member in thestate where the spring is not deformed, α is the thrust constant [N/A]of the linear motor, I is the measured value [A] of the driving currentapplied to the linear motor, β is the Bohr cross-section [m·m] of thepiston, P(t) is the pressure [Pa] in the compression chamber, and Ps isthe gas pressure (inlet pressure) [Pa] at the piston rear side.

[0226] When the linear compressor 103 is being driven in the resonancestate of the piston reciprocating motion, the pressure in thecompression chamber becomes equal to the inlet pressure when the pistonreaches the bottom dead point position. Therefore, at this point oftime, the second term on the right side of motion equation (10)indicating the piston motion becomes zero.

[0227] Further, as shown in FIG. 3, when the bottom dead point position,i.e., the piston displacement, becomes maximum, the acceleration alsobecomes maximum, whereby the driving current Id of the linear motorbecomes zero.

[0228] Accordingly, the acceleration a in the first term on the leftside of equation (10) becomes the maximum acceleration value (a=am), thevariable y″ in the second term on the left side becomes the displacementof the bottom dead point position (y″=ybd″), and the first term on theright side and the second term on the right side become zero (I=0),whereby equation (11) holds instead of equation (10).

m×a _(m) +k×y _(bd″)=0  (11)

[0229] In equation (11), am is the maximum value of piston acceleration[m/s/s], and ybd″ is the displacement [m] of the bottom dead pointposition which is indicated relative to the piston neutral positionPini.

[0230] Accordingly, when the maximum value am[m/s/s] of pistonacceleration is determined, the displacement ybd″[m] indicating thebottom dead point position (refer to FIG. 10) can be determined fromequation (11).

[0231] Next, how to determine the maximum value am[m/s/s] of pistonacceleration will be described.

[0232] The piston acceleration a is expressed by a sinusoidal functionin which time t is a variable, like the piston displacement x(t) and thepiston velocity v(t) which are described for the second embodiment.

[0233] To be specific, assuming that the angular velocity of pistonmotion is ω[rad/sec], the maximum amplitude value of piston accelerationis am[m/s/s], and the instantaneous value of piston acceleration isa(t)[m/s/s], since acceleration is a differentiated value of velocity,the piston acceleration is expressed by equation (12) with time t[sec]being a variable. $\begin{matrix}\begin{matrix}{a_{(t)} = {a_{m} \times \cos \quad {\omega \cdot t}}} \\{= \left( v_{(t)} \right)^{\prime}} \\{= {\omega \times v_{m} \times \cos \quad {\omega \cdot t}}}\end{matrix} & (12)\end{matrix}$

[0234] Since it is evident from equation (12) that the relationshipam=vm×ω holds, the maximum value am[m/s/s] of piston acceleration isobtained by the product of the maximum amplitude value vm[m/s] of thepiston velocity and the angular velocity ω [rad/sec] of the pistonmotion.

[0235] The inverter controller 6 according to the third embodimentadjusts the pulse width of the PWM signal Scp for switching the inverter2, on the basis of the resonance frequency information Irf, and outputsthe pulse width adjusted PWM signal Scp as an inverter driving controlsignal to the inverter 2 and, furthermore, outputs the information(inverter driving frequency information) Idf indicating the outputvoltage of the inverter 2 and the frequency of the output current of theinverter 2, which are determined according to the pulse width of the PWMsignal Scp, as the inverter driving frequency Fd, to the bottom deadpoint position calculation means 51.

[0236] Then, in the linear compressor driving apparatus 103 according tothe third embodiment, the bottom dead point position calculation means51 receives the piston velocity information Ipve outputted from thepiston velocity calculation means 8 and the inverter driving frequencyinformation Idf outputted from the inverter controller 6, and performsmultiplication of the maximum amplitude vm[m/s] of the piston velocityindicated by the piston velocity information Ipve, and the operatingangular velocity ω[rad/sec] (a value obtained by multiplying theinverter driving frequency Fd[Hz] indicated by the inverter drivingfrequency information Idf, with 2π), thereby obtaining the maximumamplitude am[m/s/s] of acceleration. Further, the bottom dead pointposition calculation means 51 performs multiplication of theacceleration maximum amplitude am[m/s/s] and the total mass m[kg] of themovable member, and division for diving a value obtained by themultiplication with the spring constant k[N/m] of the support spring ofthe linear compressor 100, thereby obtaining the displacement ybd″[m]indicating the bottom dead point position Pbd (refer to FIG. 10). Then,the bottom dead point position calculation means 51 outputs informationindicating the displacement ybd″[m] as bottom dead point positioninformation Ibdc.

[0237] As described above, the linear compressor driving apparatus 103according to the third embodiment is provided with the bottom dead pointposition calculation means 51 for calculating a value ybd″[m] indicatingthe distance between the piston neutral position Pini and the pistonbottom dead point position Pbd, as a piston displacement indicating thepiston bottom dead point position Pbd, on the basis of the maximumamplitude vm[m/s] of the piston velocity obtained by the piston velocitycalculation means 8, and the inverter driving frequency Fd determinedfrom the resonance frequency Fr of the linear compressor, whereby theamount of flexure of the resonance spring can be grasped by the pistonbottom dead point position information. The amount of flexure of theresonance spring is useful in drive-controlling the linear compressor soas to prevent the resonance spring from being deformed beyond thedestruction limit.

[0238] (Embodiment 4)

[0239]FIG. 6 is a block diagram for explaining a linear compressordriving apparatus according to a fourth embodiment of the presentinvention.

[0240] A linear compressor driving apparatus 104 according to the fourthembodiment is provided with a power supply 1, an inverter 2, a currentsensor 9, an output current detection means 3, a resonance frequencyinformation output means 5, an inverter controller 6, and a timingdetection means 7, like the linear compressor 101 according to the firstembodiment. Further, it is provided with a center position calculationmeans 61 for calculating a displacement yav″ of the piston amplitudecenter position Pav with respect to the piston neutral position Pini(refer to FIG. 10), as information indicating a center position Pav ofpiston reciprocating motion (piston amplitude center position) Pav, onthe basis of a detection result (driving current detection signal) Dcdfrom the output current detection means 3; and an open/close switch 11for controlling supply and supply stop of the driving current detectionsignal Dcd to the center position calculation means 61, according to aswitch control signal Scs outputted from the timing detection means 7.

[0241] The open/close switch 11 has an input side node 11 a to which thedriving current detection signal Dcd is applied from the output currentdetection means 3, and an output side not 11 b from which the drivingcurrent detection signal Dcd is output to the center positioncalculation means 61, and the switch 11 connects or disconnects theinput side node 11 a to/from the output side node 11 b, on the basis ofthe switch control signal Scs that is a detection result from the timingdetection means 7.

[0242] In this fourth embodiment, the center position calculation means61 is implemented by software. However, the center position calculationmeans 61 may be constituted by hardware.

[0243] Next, the operation will be described.

[0244] According to this fourth embodiment, like the first embodiment,in the linear compressor 100, the linear motor is driven with the acvoltage Vd supplied from the inverter 2, whereby the pistonreciprocates. Further, since the frequency of the ac current Vd appliedto the linear compressor matches the resonance frequency Fr of pistonreciprocating motion, the linear compressor 100 is driven in theresonance state of piston reciprocating motion.

[0245] At this time, in the output current detection means 3, theinverter output current, i.e., the driving current Id of the linearcompressor 100, is detected on the basis of the current monitoringoutput Scm from the current sensor 9, and a detection result (drivingcurrent detection signal) Dcd is output to the input side node 11 a ofthe open/close switch 11.

[0246] Further, in the timing detection means 7, a phase timing at whichthe phase of the inverter driving current Id becomes at least one of 90°and 270° is detected on the basis of the current monitoring output Scmfrom the current sensor 9, and a switch control signal Scs forconnecting the input side node 11 a and the output side node 11 b of theopen/close switch 11 is output to the open/close switch 11 at this phasetiming.

[0247] In the open/close switch 11, on receipt of the switch controlsignal Scs, the corresponding input side node and output side node areconnected at the phase timing, whereby a value (instantaneous value) I1of the driving current Id at the phase timing is output to the centerposition calculation means 61.

[0248] Then, in the center position calculation means 61, a displacementyav″[m] of the piston amplitude center position Pav relative to thepiston neutral position Pini is calculated from the following formula(13), on the basis of the instantaneous value Im of the driving currentat the phase timing, and information indicating the displacement yav″ isoutput as amplitude center position information Iav.

[0249] That is, as described in the third embodiment, as for the pistonreciprocating motion by the linear motor of the linear compressor 100,the above-described equation (10) holds as a motion equation.

[0250] With the phase timing at which the phase of the driving currentapplied to the linear compressor becomes at least one of 90° and 270° insuch piston reciprocating motion, the piston acceleration a[m/s/s]becomes zero, and the displacement y″[m] of the piston position Prelative to the piston neutral position Pini matches the displacementyav″ of the piston amplitude center position Pav relative to the pistonneutral position Pini, and further, the driving current I[A] takes themaximum value Im.

[0251] In this fourth embodiment, the linear compressor 100 is designedso that the inlet valve of the linear compressor 100 is opened at theabove-mentioned phase timing, and the pressure P(t)[Pa] in thecompression chamber becomes equal to the inlet pressure Ps[Pa], andtherefore, the following equation (13) holds instead of equation (10).

k×y _(av″) =α×I _(m)  (13)

[0252] From equation (13), the displacement yav″[m] of the pistonamplitude center position Pav can be obtained by arithmetic processingin which the product of the maximum amplitude Im[A] of the input currentto the linear compressor and the thrust constant α[N/A] of the linearmotor is divided by the spring constant k[N/m] of the support spring ofthe linear compressor.

[0253] As described above, the linear compressor driving apparatus 104according to the fourth embodiment is provided with the center positioncalculation means 61 instead of the output voltage detection means 4 andthe piston velocity detection means 8 in the linear compressor drivingapparatus 101 according to the first embodiment, which calculation means61 calculates the displacement yav″ indicating the piston amplitudecenter position, on the basis of the instantaneous value Im[A] of thedriving current at the phase timing in which the phase of the linearcompressor driving current Id is at least one of 90° and 270°.Therefore, the displacement yav″ of the center position Pav of pistonreciprocating motion with respect to the piston neutral position Pinican be accurately obtained by relatively simple arithmetic processingincluding only multiplication and division, whereby detection of thecenter position Pav of piston reciprocating motion can be easily carriedout with high accuracy.

[0254] Furthermore, in this fourth embodiment, the linear compressordriving apparatus 104 detects the instantaneous value Im of the inverterdriving current Id with the phase timing at which the phase of theinverter driving current Id becomes at least one of 90° and 270°, andcalculates the piston amplitude center position information on the basisof the instantaneous value Im. However, the linear compressor drivingapparatus 104 may calculate the piston amplitude center positioninformation, on the basis of the instantaneous value Im of the inverterdriving current Id, the pressure of the cooling medium gas dischargedfrom the linear compressor, and the pressure of the cooling medium gasdrawn into the linear compressor.

[0255] In this case, the linear compressor driving apparatus accordingto the fourth embodiment is further provided with a discharge pressuredetection means for detecting the pressure of the cooling medium gasdischarged from the linear compressor, and an inlet pressure detectionmeans for detecting the pressure of the cooling medium gas drawn intothe linear compressor, and the center position information calculationmeans calculates an action force in the direction of the pistonreciprocating motion, which force acts on the piston from the coolingmedium gas, on the basis of a pressure difference between the dischargepressure and the inlet pressure, and further, it calculates positioninformation indicating the piston center position relative to the pistonposition in which the pressure difference becomes zero, as the centerposition information.

[0256] Furthermore, the center position information calculation meansmay calculate an action force in the direction of the pistonreciprocating motion, which acts on the piston from the cooling mediumgas, on the basis of a pressure difference between the dischargepressure and the inlet pressure, and the resonance frequency indicatedby the resonance frequency information outputted from the resonancefrequency information output means 5, and it may calculate positioninformation indicating the piston center position relative to the pistonposition in which the pressure difference becomes zero, as the centerposition information.

APPLICABILITY IN INDUSTRY

[0257] As described above, the linear compressor driving apparatusaccording to the present invention can accurately detect the stroke andtop clearance of the piston of the linear compressor, in relativelysimple arithmetic processing, without using a position sensor.Therefore, the linear compressor driving apparatus is very useful as adriving apparatus for a linear compressor in which the stroke and topclearance of a piston vary with variations of loads, and it is used fora refrigerating compressor.

1. A linear compressor driving apparatus for driving a linear compressorwhich has a piston and a linear motor for making the piston reciprocate,and generates a compressed gas by the reciprocating motion of thepiston, with an AC voltage being applied to the linear motor, saidapparatus comprising: an inverter for outputting an AC voltage and an ACcurrent to the linear motor; a resonance frequency information outputmeans for outputting resonance frequency information which indicates aresonance frequency of the reciprocating motion of the piston; a voltagedetection means for detecting an output voltage of the inverter tooutput a voltage detection signal; a current detection means fordetecting an output current of the inverter to output a currentdetection signal; an inverter controller for controlling the inverter onthe basis of the resonance frequency information so that the inverteroutputs, as its output voltage and output current, asinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped currentwhose frequencies match the resonance frequency of the pistonreciprocating motion, respectively; a timing detection means fordetecting, as a specific phase timing, a phase timing at which adifferentiated value of the output current of the inverter becomes zero;and a piston velocity calculation means for receiving the voltagedetection signal and the current detection signal, and calculating amaximum amplitude of a piston velocity in the piston reciprocatingmotion, on the basis of instantaneous values of the output voltage andthe output current from the inverter at the specific phase timing.
 2. Alinear compressor driving apparatus as defined in claim 1, wherein thetiming detection means detects, as the specific phase timing, a phasetiming at which the amplitude of the output current from the inverterbecomes maximum.
 3. A linear compressor driving apparatus as defined inclaim 1, wherein the timing detection means detects a phase timing atwhich the phase of the output AC current from the inverter becomes atleast one of 90° and 270°, as the specific phase timing, on the basis ofthe current detection signal.
 4. A linear compressor driving apparatusas defined in claim 3, wherein the inverter is provided with an invertercontroller for outputting an inverter driving control signal whichdrives and controls the inverter; and the timing detection means detectsa phase timing at which a differentiated value of the output currentfrom the inverter becomes zero, on the basis of the phase of theinverter driving control signal.
 5. A linear compressor drivingapparatus as defined in claim 4, wherein the timing detection means hasa phase shift amount detector for detecting the amount of phase shift ofthe phase of the inverter driving control signal from the phase of theoutput current of the inverter, and detects a phase timing at which adifferentiated value of the output current of the inverter becomes zero,on the basis of the inverter driving control signal whose phase iscorrected so that the amount of phase shift becomes zero.
 6. A linearcompressor driving apparatus as defined in claim 1, wherein the pistonvelocity calculation means performs a temperature correction process ona thrust constant of the linear motor, whose value varies withvariations in temperature, and calculates a maximum amplitude of thepiston velocity on the basis of the temperature-corrected thrustconstant, the instantaneous current value, the instantaneous voltagevalue, and an internal resistance value of the linear motor.
 7. A linearcompressor driving apparatus as defined in claim 1, wherein the pistonvelocity calculation means performs a temperature correction process onan internal resistance value of the linear motor, whose value varieswith variations in temperature, and calculates a maximum amplitude ofthe piston velocity on the basis of the temperature-corrected internalresistance value, the instantaneous values of the output voltage andoutput current of the inverter, and a thrust constant of the linearmotor.
 8. A linear compressor driving apparatus as defined in claim 1,wherein the piston velocity calculation means repeats a velocitycalculation process for calculating a maximum amplitude of the pistonvelocity, and in each of the repeated velocity calculation processes,the piston velocity calculation means corrects a thrust constant of thelinear motor, whose value varies with variations in the piston velocity,on the basis of a maximum amplitude of the piston velocity which iscalculated in the previous velocity calculation process, and calculatesa maximum amplitude of the piston velocity on the basis of the correctedthrust constant.
 9. A linear compressor driving apparatus as defined inclaim 1 further including a stroke information calculation means forcalculating piston stroke information which indicates a maximumamplitude of a piston displacement in the piston reciprocating motion,on the basis of the output voltage of the inverter and the frequency ofthe output current of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity that iscalculated by the piston velocity calculation means.
 10. A linearcompressor driving apparatus as defined in claim 1 further including abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity that iscalculated by the piston velocity calculation means.
 11. A linearcompressor driving apparatus as defined in claim 9 further including: abottom dead point position information calculation means for calculatingbottom dead point position information which indicates a piston bottomdead point position in the piston reciprocating motion, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity that iscalculated by the piston velocity calculation means; and an arithmeticmeans for calculating center position information which indicates apiston center position in the piston reciprocating motion, by performingthe four fundamental rules of arithmetic on the basis of the bottom deadpoint position information and the piston stroke information.
 12. Alinear compressor driving apparatus as defined in claim 9 furtherincluding: a bottom dead point position information calculation meansfor calculating bottom dead point position information which indicates apiston bottom dead point position in the piston reciprocating motion, onthe basis of the output voltage of the inverter and the frequency of theoutput current of the inverter, which are determined by the invertercontroller, and the maximum amplitude of the piston velocity which iscalculated by the piston velocity calculation means; and an arithmeticmeans for calculating top dead point position information indicating apiston top dead point position in the piston reciprocating motion, byperforming the four fundamental rules of arithmetic on the basis of thebottom dead point position information and the piston strokeinformation.
 13. A linear compressor driving apparatus as defined inclaim 9 further including: a top dead point position informationdetection sensor for detecting a piston top dead point position in thepiston reciprocating motion to output top dead point positioninformation indicating the detected position; and an arithmetic meansfor calculating center position information indicating a piston centerposition in the piston reciprocating motion, by performing the fourfundamental rules of arithmetic on the basis of the top dead pointposition information and the piston stroke information.
 14. A linearcompressor driving apparatus as defined in claim 9 further including: atop dead point position information detection sensor for detecting apiston top dead point position in the piston reciprocating motion tooutput top dead point position information indicating the detectedposition; and an arithmetic means for calculating bottom dead pointposition information indicating a piston bottom dead point position inthe piston reciprocating motion, by performing the four fundamentalrules of arithmetic on the basis of the top dead point positioninformation and the piston stroke information.
 15. A linear compressordriving apparatus as defined in claim 9 further including: a bottom deadpoint position information detection sensor for detecting a pistonbottom dead point position in the piston reciprocating motion; and anarithmetic means for calculating center position information indicatinga piston center position in the piston reciprocating motion, byperforming the four fundamental rules of arithmetic on the basis of thebottom dead point position information and the piston strokeinformation.
 16. A linear compressor driving apparatus as defined inclaim 9 further including: a bottom dead point position informationdetection sensor for detecting a piston bottom dead point position inthe piston reciprocating motion to output bottom dead point positioninformation indicating the detected position; and an arithmetic meansfor calculating top dead point position information indicating a pistontop dead point position in the piston reciprocating motion, byperforming the four fundamental rules of arithmetic on the basis of thebottom dead point position information and the piston strokeinformation.
 17. A linear compressor driving apparatus as defined inclaim 9 further including: a center position information calculationmeans for calculating center position information indicating a pistoncenter position in the piston reciprocating motion, on the basis of theoutput current from the inverter; and an arithmetic means forcalculating top dead point position information indicating a piston topdead point position in the piston reciprocating motion, by performingthe four fundamental rules of arithmetic on the basis of the centerposition information and the piston stroke information.
 18. A linearcompressor driving apparatus as defined in claim 9 further including: acenter position information calculation means for calculating centerposition information indicating a piston center position in the pistonreciprocating motion, on the basis of the output current from theinverter; and an arithmetic means for calculating bottom deal pointposition information indicating a piston bottom dead point position inthe piston reciprocating motion, by performing the four fundamentalrules of arithmetic on the basis of the center position information andthe piston stroke information.
 19. A linear compressor driving apparatusas defined in any of claims 10 to 12, wherein the linear compressor hasan elastic member which applies a force to the piston so as to bring thepiston back to its neutral position, when the piston is displaced fromthe neutral position; and the bottom dead point position informationcalculation means calculates, as the bottom dead point positioninformation, position information indicating the piston bottom deadpoint position relative to the piston neutral position, on the basis ofthe output voltage of the inverter and the frequency of the outputcurrent of the inverter, which are determined by the invertercontroller, the maximum amplitude of the piston velocity which iscalculated by the piston velocity calculation means, the weight of themovable member which performs the piston reciprocating motion in thelinear compressor, and the spring constant of the elastic member.
 20. Alinear compressor driving apparatus as defined in claim 9, wherein thepiston stroke calculation means repeats a calculation process forcalculating the piston stroke information on the basis of the maximumamplitude of the piston velocity, and in each of the repeatedcalculation processes, the piston stroke calculation means corrects athrust constant of the linear motor, whose value varies with variationsin the piston position, on the basis of the piston stroke informationcalculated in the previous calculation process, and calculates thepiston stroke information on the basis of the corrected thrust constant.21. A linear compressor driving apparatus for driving a linearcompressor which has a piston and a linear motor for reciprocating thepiston, and generates a compressed gas by the reciprocating motion ofthe piston, with an AC voltage being applied to the linear motor, saidapparatus comprising: an inverter for outputting an AC voltage and an ACcurrent to the linear motor; a resonance frequency information outputmeans for outputting resonance frequency information that indicates aresonance frequency of the piston reciprocating motion; a currentdetection means for detecting an output current of the inverter tooutput a current detection signal; an inverter controller for controllerthe inverter on the basis of the resonance frequency information so thatthe inverter outputs, as its output voltage and output current, asinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped currentwhose frequencies match the resonance frequency of the pistonreciprocating motion, respectively; a timing detection means fordetecting, as a specific phase timing, a phase timing at which adifferentiated value of the output current of the inverter becomes zero;and a piston center position calculation means for calculating positioninformation indicating a piston center position in the pistonreciprocating motion, on the basis of an instantaneous value of theoutput current of the inverter at the specific phase timing, withreference to a piston position where a pressure difference between thepressure of a cooling medium gas that is discharged from the linearcompressor and the pressure of the cooling medium gas that is drawn intothe linear compressor becomes zero.
 22. A linear compressor drivingapparatus as defined in claim 21, wherein the linear compressor has anelastic member which applies a force to the piston so as to bring thepiston back to its neutral position, when the piston is displaced fromthe neutral position; and the center position information calculationmeans calculates, as the center position information, positioninformation indicating the piston center position relative to the pistonneutral position, on the basis of the maximum amplitude of the outputcurrent from the inverter, the thrust constant of the linear motor, andthe spring constant of the elastic member.
 23. A linear compressordriving apparatus as defined in claim 21 further including: a dischargepressure detection means for detecting the pressure of the coolingmedium gas that is discharged from the linear compressor; and an inletpressure detection means for detecting the pressure of the coolingmedium gas that is drawn into the linear compressor; wherein the centerposition information calculation means calculates an action force in thedirection of the piston reciprocating motion, which force acts on thepiston from the cooling medium gas, on the basis of the pressuredifference between the discharge pressure and the inlet pressure, andthen calculates, as the center position information, positioninformation indicating the piston center position relative to the pistonposition where the pressure difference becomes zero, on the basis of thecalculated action force.
 24. A linear compressor driving apparatus asdefined in claim 23, wherein the center position information calculationmeans calculates an action force in the direction of the pistonreciprocating motion, which force acts on the piston from the coolingmedium gas, on the basis of the pressure difference between thedischarge pressure and the inlet pressure, and the resonance frequencyindicated by the resonance frequency information, and then calculates,as the center position information, position information indicating thepiston center position relative to the piston position where thepressure difference becomes zero, on the basis of the calculated actionforce.